TY - JOUR A1 - Klamroth, Tillmann A1 - Nest, Mathias T1 - Ultrafast electronic excitations of small sodium clusters and the onset of electron thermalization N2 - In this paper we report simulations of the ultrafast laser excitation and relaxation of the correlated valence electrons of a Na-8 cluster. The aim is twofold: first, while the total energy stays constant when the exciting laser pulse is over, we observe that the entropy computed from the reduced one electron density matrix rises on a much longer time scale. We discuss whether this can be understood as the onset of the thermalization of a finite system. Second, we describe this process with eight different methods of wavefunction-based electronic structure theory, which have been adapted for an explicitly time-dependent description. Their respective advantages and limitations for the simulation of the excitation and subsequent relaxation are explained. Y1 - 2009 UR - http://pubs.rsc.org/en/Journals/JournalIssues/CP U6 - https://doi.org/10.1039/B813619j SN - 1463-9076 ER - TY - JOUR A1 - Tremblay, Jean Christophe A1 - Krause, Pascal A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Time-dependent response of dissipative electron systems N2 - We present a systematic study of the influence of energy and phase relaxation on dynamic polarizability simulations in the linear response regime. The nonperturbative approach is based on explicit electron dynamics using short laser pulses of low intensities. To include environmental effects on the property calculation, we use the time- dependent configuration-interaction method in its reduced density matrix formulation. Both energy dissipation and nonlocal pure dephasing are included. The explicit treatment of time-resolved electron dynamics gives access to the phase shift between the electric field and the induced dipole moment, which can be used to define a useful uncertainty measure for the dynamic polarizability. The nonperturbative treatment is compared to perturbation theory expressions, as applied to a simple model system, the rigid H-2 molecule. It is shown that both approaches are equivalent for low field intensities, but the time-dependent treatment provides complementary information on the phase of the induced dipole moment, which allows for the definition of an uncertainty associated with the computation of the dynamic polarizability in the linear response regime. Y1 - 2010 UR - http://pra.aps.org/ U6 - https://doi.org/10.1103/Physreva.81.063420 SN - 1050-2947 ER - TY - JOUR A1 - Krause, Pascal A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Time-dependent configuration-interaction calculations of laser-pulse-driven many-electron dynamics : Controlled dipole switching in lithium cyanide N2 - We report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (doubles) approach. The method accounts for the correlation of ground and excited states, is capable of describing explicitly time-dependent, nonlinear phenomena, and is systematically improvable. Lithium cyanide serves as a molecular test system in which the charge distribution and hence the dipole moment are shown to be switchable, in a controlled fashion, by (a series of) laser pulses which induce selective, state-to-state electronic transitions. One focus of our time-dependent calculations is the question of how fast the transition from the ionic ground state to a specific excited state that is embedded in a multitude of other states can be made, without creating an electronic wave packet. (c) 2005 American Institute of Physics Y1 - 2005 SN - 0021-9606 ER - TY - JOUR A1 - Ehlert, Christopher A1 - Klamroth, Tillmann T1 - The quest for best suited references for configuration interaction singles calculations of core excited states JF - Journal of computational chemistry : organic, inorganic, physical, biological N2 - Near edge X-ray absorption fine structure (NEXAFS) simulations based on the conventional configuration interaction singles (CIS) lead to excitation energies, which are systematically blue shifted. Using a (restricted) open shell core hole reference instead of the Hartree Fock (HF) ground state orbitals improves (Decleva et al., Chem. Phys., 1992, 168, 51) excitation energies and the shape of the spectra significantly. In this work, we systematically vary the underlying SCF approaches, that is, based on HF or density functional theory, to identify best suited reference orbitals using a series of small test molecules. We compare the energies of the K edges and NEXAFS spectra to experimental data. The main improvement compared to conventional CIS, that is, using HF ground state orbitals, is due to the electrostatic influence of the core hole. Different SCF approaches, density functionals, or the use of fractional occupations lead only to comparably small changes. Furthermore, to account for bigger systems, we adapt the core-valence separation for our approach. We demonstrate that the good quality of the spectrum is not influenced by this approximation when used together with the non-separated ground state wave function. Simultaneously, the computational demands are reduced remarkably. (C) 2016 Wiley Periodicals, Inc. KW - core excited states KW - configuration interaction KW - near edge X-ray absorption fine structure Y1 - 2016 U6 - https://doi.org/10.1002/jcc.24531 SN - 0192-8651 SN - 1096-987X VL - 38 SP - 116 EP - 126 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Nest, Mathias A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - The multiconfiguration time-dependent Hartree-Fock method for quantum chemical calculations N2 - We apply the multiconfiguration time-dependent Hartree-Fock method to electronic structure calculations and show that quantum chemical information can be obtained with this explicitly time-dependent approach. Different equations of motion are discussed, as well as the numerical cost. The two-electron integrals are calculated using a natural potential expansion, of which we describe the convergence behavior in detail Y1 - 2005 SN - 0021-9606 ER - TY - JOUR A1 - Balischewski, Christian A1 - Bhattacharyya, Biswajit A1 - Sperlich, Eric A1 - Günter, Christina A1 - Beqiraj, Alkit A1 - Klamroth, Tillmann A1 - Behrens, Karsten A1 - Mies, Stefan A1 - Kelling, Alexandra A1 - Lubahn, Susanne A1 - Holtzheimer, Lea A1 - Nitschke, Anne A1 - Taubert, Andreas T1 - Tetrahalidometallate(II) ionic liquids with more than one metal BT - the effect of bromide versus chloride JF - Chemistry - a European journal N2 - Fifteen N-butylpyridinium salts - five monometallic [C4Py](2)[MBr4] and ten bimetallic [C4Py](2)[(M0.5M0.5Br4)-M-a-Br-b] (M=Co, Cu, Mn, Ni, Zn) - were synthesized, and their structures and thermal and electrochemical properties were studied. All the compounds are ionic liquids (ILs) with melting points between 64 and 101 degrees C. Powder and single-crystal X-ray diffraction show that all ILs are isostructural. The electrochemical stability windows of the ILs are between 2 and 3 V. The conductivities at room temperature are between 10(-5) and 10(-6) S cm(-1). At elevated temperatures, the conductivities reach up to 10(-4) S cm(-1) at 70 degrees C. The structures and properties of the current bromide-based ILs were also compared with those of previous examples using chloride ligands, which illustrated differences and similarities between the two groups of ILs. KW - electrochemistry KW - ionic liquids KW - metal-containing ionic liquids; KW - N-butylpyridinium bromide KW - tetrahalidometallates Y1 - 2022 U6 - https://doi.org/10.1002/chem.202201068 SN - 1521-3765 VL - 28 IS - 64 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Farra, Ramzi A1 - Thiel, Kerstin A1 - Winter, Alette A1 - Klamroth, Tillmann A1 - Poeppl, Andreas A1 - Kelling, Alexandra A1 - Schilde, Uwe A1 - Taubert, Andreas A1 - Strauch, Peter T1 - Tetrahalidocuprates(II)-structure and EPR spectroscopy Part 1: Tetrabromidocuprates(II) JF - New journal of chemistry N2 - Tetrahalidocuprates(II) show a high degree of structural flexibility. We present the results of crystallographic and electron paramagnetic resonance (EPR) spectroscopic analyses of four new tetrabromidocuprate(II) compounds and compare the results with previously reported data. The cations in the new compounds are the sterically demanding benzyltriphenylphosphonium, methyltriphenylphosphonium, tetraphenylphosphonium, and hexadecyltrimethylammonium ions; they were used to achieve a reasonable separation of the paramagnetic Cu(II) ions for EPR spectroscopy. X-Ray crystallography shows that in all four complexes the [CuBr4](2-) units have a distorted tetrahedral coordination geometry which is in agreement with DFT calculations. The EPR hyperfine structure was not resolved. This is due to the exchange broadening resulting from still incomplete separation of the paramagnetic Cu(II) centres. Nevertheless, the principal values of the electron Zeemann tensor (g(parallel to) and g(perpendicular to)) of the complexes could be determined. A correlation of structural (X-ray) parameters with the spin density at the copper centres (DFT) is well reflected in the EPR spectra of the bromidocuprates. This enables the correlation of X-ray and EPR parameters to predict the structure of tetrabromidocuprates in physical states other than the crystalline state. As a result, we provide a method to structurally characterize [CuBr4](2-) in, for example, ionic liquids or in solution, which has important implications for e.g. catalysis or materials science. Y1 - 2011 U6 - https://doi.org/10.1039/c1nj20271e SN - 1144-0546 VL - 35 IS - 12 SP - 2793 EP - 2803 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Winter, Alette A1 - Thiel, Kerstin A1 - Zabel, André A1 - Klamroth, Tillmann A1 - Pöppl, Andreas A1 - Kelling, Alexandra A1 - Schilde, Uwe A1 - Taubert, Andreas A1 - Strauch, Peter T1 - Tetrahalidocuprates(II) – structure and EPR spectroscopy BT - Part 2: tetrachloridocuprates(II) N2 - We present and discuss the results of crystallographic and electron paramagnetic resonance (EPR) spectroscopic analyses of five tetrachloridocuprate(II) complexes to supply a useful tool for the structural characterisation of the [CuCl4]2− moiety in the liquid state, for example in ionic liquids, or in solution. Bis(benzyltriethylammonium)-, bis(trimethylphenylammonium)-, bis(ethyltriphenylphosphonium)-, bis(benzyltriphenylphosphonium)-, and bis(tetraphenylarsonium)tetrachloridocuprate(II) were synthesised and characterised by elemental, IR, EPR and X-ray analyses. The results of the crystallographic analyses show distorted tetrahedral coordination geometry of all [CuCl4]2− anions in the five complexes and prove that all investigated complexes are stabilised by hydrogen bonds of different intensities. Despite the use of sterically demanding ammonium, phosphonium and arsonium cations to obtain the separation of the paramagnetic Cu(II) centres for EPR spectroscopy no hyperfine structure was observed in the EPR spectra but the principal values of the electron Zeeman tensor, g∥ and g⊥, could be determined. With these EPR data and the crystallographic parameters we were able to carry out a correlation study to anticipate the structural situation of tetrachloridocuprates in different physical states. This correlation is in good agreement with DFT calculations. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 240 KW - electron-spin resonance KW - liquid-crystal precursors KW - copper(II) halide salts KW - ionic liquid KW - square planar KW - tetrachlorocuprate(II) salts KW - molecular-structure KW - magnetic-properties KW - paramagnetic-resonance KW - temperature phase Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95012 SP - 1019 EP - 1030 ER - TY - JOUR A1 - Winter, Alette A1 - Thiel, Kerstin A1 - Zabel, Andre A1 - Klamroth, Tillmann A1 - Poeppl, Andreas A1 - Kelling, Alexandra A1 - Schilde, Uwe A1 - Taubert, Andreas A1 - Strauch, Peter T1 - Tetrahalidocuprates(II) - structure and EPR spectroscopy. Part 2: tetrachloridocuprates(II) JF - New journal of chemistry N2 - We present and discuss the results of crystallographic and electron paramagnetic resonance (EPR) spectroscopic analyses of five tetrachloridocuprate(II) complexes to supply a useful tool for the structural characterisation of the [CuCl4](2-) moiety in the liquid state, for example in ionic liquids, or in solution. Bis(benzyltriethylammonium)-, bis(trimethylphenylammonium)-, bis(ethyltriphenylphosphonium)-, bis(benzyltriphenylphosphonium)-, and bis(tetraphenylarsonium) tetrachloridocuprate(II) were synthesised and characterised by elemental, IR, EPR and X-ray analyses. The results of the crystallographic analyses show distorted tetrahedral coordination geometry of all [CuCl4](2-) anions in the five complexes and prove that all investigated complexes are stabilised by hydrogen bonds of different intensities. Despite the use of sterically demanding ammonium, phosphonium and arsonium cations to obtain the separation of the paramagnetic Cu(II) centres for EPR spectroscopy no hyperfine structure was observed in the EPR spectra but the principal values of the electron Zeeman tensor, g(parallel to) and g(perpendicular to), could be determined. With these EPR data and the crystallographic parameters we were able to carry out a correlation study to anticipate the structural situation of tetrachloridocuprates in different physical states. This correlation is in good agreement with DFT calculations. Y1 - 2014 U6 - https://doi.org/10.1039/c3nj01039b SN - 1144-0546 SN - 1369-9261 VL - 38 IS - 3 SP - 1019 EP - 1030 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schwarze, Thomas A1 - Mickler, Wulfhard A1 - Dosche, Carsten A1 - Flehr, Roman A1 - Klamroth, Tillmann A1 - Löhmannsröben, Hans-Gerd A1 - Saalfrank, Peter A1 - Holdt, Hans-Jürgen T1 - Systematic investigation of photoinduced electron transfer controlled by internal charge transfer and its consequences for selective PdCl2 coordination N2 - Fluoroionophores of fluorophore-spacer-receptor format were prepared for detection of PdCl2 by fluorescence enhancement. The fluorophore probes 1-13 consist of a fluorophore group, in alkyl spacer and a dithiomaleonitrile PdCl2 receptor. First, varying the length of the alkylene spacer (compounds 1-3) revealed, dominant through-space pathway for oxidative photoinduced electron transfer (PET) in CH2-bridged dithiomaleonitrile fluoroionophores. Second. fluorescent probes 4-9 containing two anthracene or pyrene fragments connected through CH2 bridges to the dithiomaleonitrile unit were synthesized. Modulation of the oxidation potential (E-Ox) through electron-withdrawing or -donating groups on the anthracene moiety regulates file thermodynamic driving force for oxidative PET (Delta G(PET)) in bis(anthrylmethylthio)maleonitriles and therefore the fluorescence quantum yields (Phi(f)), too. The new concept was confirmed and transferred to pyrenyl ligands, and fluorescence enhancements (FE) greater than 3.2 in the presence of PdCl2 were achieved by 7 and 8 (FE=5.4 and 5.2). Finally, for comparison, monofluorophore ligands 10-13 were synthesized. Y1 - 2010 UR - http://onlinelibrary.wiley.com/doi/10.1002/chem.200902281/pdf U6 - https://doi.org/10.1002/chem.200902281 SN - 0947-6539 ER - TY - JOUR A1 - Schwarze, Thomas A1 - Mickler, Wulfhard A1 - Dosche, Carsten A1 - Flehr, Roman A1 - Klamroth, Tillmann A1 - Löhmannsröben, Hans-Gerd A1 - Saalfrank, Peter A1 - Holdt, Hans-Jürgen T1 - Systematic investigation of photoinduced electron transfer controlled by internal charge transfer and its consequences for selective PdCl2 coordination N2 - Fluoroionophores of fluorophore-spacer-receptor format were prepared for detection of PdCl2 by fluorescence enhancement. The fluorescent probes 1-13 consist of a fluorophore group, an alkyl spacer and a dithiomaleonitrile PdCl2 receptor. First, varying the length of the alkylene spacer (compounds 1-3) revealed a dominant through-space pathway for oxidative photoinduced electron transfer (PET) in CH2-bridged dithiomaleonitrile fluoroionophores. Second, fluorescent probes 4-9 containing two anthracene or pyrene fragments connected through CH2 bridges to the dithiomaleonitrile unit were synthesized. Modulation of the oxidation potential (EOx) through electron-withdrawing or -donating groups on the anthracene moiety regulates the thermodynamic driving force for oxidative PET (GPET) in bis(anthrylmethylthio)maleonitriles and therefore the fluorescence quantum yields (f), too. The new concept was confirmed and transferred to pyrenyl ligands, and fluorescence enhancements (FE) greater than 3.2 in the presence of PdCl2 were achieved by 7 and 8 (FE=5.4 and 5.2). Finally, for comparison, monofluorophore ligands 10-13 were synthesized. Y1 - 2010 UR - http://www3.interscience.wiley.com/journal/26293/home SN - 0947-6539 ER - TY - JOUR A1 - Füchsel, Gernot A1 - Klamroth, Tillmann A1 - Tremblay, Jean Christophe A1 - Saalfrank, Peter T1 - Stochastic approach to laser-induced ultrafast dynamics : the desorption of H-2/D-2 from Ru(0001) N2 - The desorption of molecular hydrogen and deuterium induced by femtosecond-laser pulses is studied theoretically for the so-called DIMET (Desorption Induced by Multiple Electronic Transitions) process. These investigations are based on nonadiabatic classical Monte Carlo trajectory (CMCT) simulations on a ground and an excited state potential energy surface, including up to all six adsorbate degrees of freedom. The focus is on the hot-electron mediated energy transfer from the surface to the molecule and back, and the energy partitioning between the different degrees of freedom of the desorbing molecules. We first validate for a two-mode model comprising the desorption mode and the internal vibrational coordinate, the classical Monte Carlo trajectory method by comparing with Monte Carlo wavepacket (MCWP) calculations arising from a fully quantum mechanical open-system density matrix treatment. We then proceed by extending the CMCT calculations to include all six nuclear degrees of freedom of the desorbing molecule. This allows for a detailed comparison between theory and experiment concerning isotope effects, energy partitioning (translational, vibrational, and rotational energies and their distributions), and the dependence of these properties on the laser fluence. The most important findings are as follows. (i) CMCT agrees qualitative with the MCWP scheme. (ii) The basic experimental features such as the large isotope effect, the non-linear increase of yield with laser fluence, translationally hot products (in the order of several 1000 K) and non-equipartitioning of translational and internal energies (E-trans > E- vib > E-rot) are well reproduced. (iii) Predictions concerning a strong angular dependence of translational energies at large observation angles are also made. Y1 - 2010 UR - http://xlink.rsc.org/jumptojournal.cfm?journal_code=CP U6 - https://doi.org/10.1039/C0cp00895h SN - 1463-9076 ER - TY - JOUR A1 - Zenichowski, Karl A1 - Nacci, Ch A1 - Fölsch, S. A1 - Dokic, Jadranka A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - STM-switching of organic molecules on semiconductor surfaces: an above threshold density matrix model for 1,5 cyclooctadiene on Si(100) JF - Journal of physics : Condensed matter N2 - The scanning tunnelling microscope (STM)-induced switching of a single cyclooctadiene molecule between two stable conformations chemisorbed on a Si(100) surface is investigated using an above threshold model including a neutral ground state and an ionic excited state potential. Switching was recently achieved experimentally with an STM operated at cryogenic temperatures (Nacci et al 2008 Phys. Rev. B 77 121405(R)) and rationalized by a below threshold model using just a single potential energy surface (Nacci et al 2009 Nano Lett. 9 2997). In the present paper, we show that experimental key findings on the inelastic electron tunnelling (IET) switching can also be rationalized using an above threshold density matrix model, which includes, in addition to the neutral ground state potential, an anionic or cationic excited potential. We use one and two-dimensional potential energy surfaces. Furthermore, the influence of two key parameters of the density matrix description, namely the electronic lifetime of the ionic resonance and the vibrational lifetimes, on the ground state potential are discussed. Y1 - 2012 U6 - https://doi.org/10.1088/0953-8984/24/39/394009 SN - 0953-8984 VL - 24 IS - 39 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Klinkusch, Stefan A1 - Klamroth, Tillmann T1 - Simulations of pump-probe exitations of electronic wave packets for a large qusi-rigid molecular system by means of an extension to the time-dependent configuration interaction singles method JF - Journal of theoretical and computational chemistry N2 - In this paper, we report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (TD-CIS) approach. Photoionization is included by a heuristic model within calculations employing standard Gaussian basis sets. Benzo[g]-N-methyl-quinolinium-7-hydroxylate (BMQ7H) serves as a test system to generate predefined wave packets, i.e. a superposition between the ground and fifth excited state, in a large molecule. For this molecule, these two states have a very similar geometry, which enables us to use the fixed nuclei approximation. Furthermore, this geometric stability would also prevent a dephasing of the electron wave packet due to nuclear dynamics in an experimental realization of our simulations. We also simulate the possible detection of such a wave packet by ultra short probe laser pulses, i.e. pump-probe spectra. KW - Electron dynamics KW - time-dependent configuration interaction KW - pump-probe Y1 - 2013 U6 - https://doi.org/10.1142/S0219633613500053 SN - 0219-6336 VL - 12 IS - 3 PB - World Scientific CY - Singapore ER - TY - JOUR A1 - Huber, C. A1 - Klamroth, Tillmann T1 - Simulation of two-photon-photoelectron spectra at a jellium-vacuum interface N2 - In this paper we report on time dependent configuration interaction singles (TD-CIS) calculations aimed at simulating two-photon-photoelectron emission (2PPE) spectra of metal films, the latter treated within a one-dimensional jellium model. The method is based on a many-electron approach in which electron-electron-scattering is approximately accounted for and no artificial lifetimes have to be assumed for excited electrons. This contrasts with one-electron models where lifetimes and "dissipation" have to be introduced. The driving force for the photoelectron ejection in 2PPE experiments is the electric field of two laser pulses that are generally separated by a delay time, Delta t. To compute energy- and time-resolved 2PPE signals P(E, Delta t), a new scheme based on the time-energy method is proposed to analyze electronic wave packets in asymptotic regions of the potential Y1 - 2005 ER - TY - JOUR A1 - Füchsel, Gernot A1 - Tremblay, Jean Christophe A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Selective excitation of molecule-surface vibrations in H2 and D2 dissociatively adsorbed on Ru(0001) JF - Israel journal of chemistry N2 - In this contribution we report about the selective vibrational excitation of H2 and D2 on Ru(0001) as an example for nonadiabatic coupling of an open quantum system to a dissipative environment. We investigate the possibility of achieving state-selective vibrational excitations of H2 and D2 adsorbed on a Ru(0001) surface using picosecond infrared laser pulses. The systems behavior is explored using pulses that are rationally designed and others that are optimized using a time-local variant of Optimal Control Theory. The effects of dissipation on the laser-driven dynamics are studied using the reduced-density matrix formalism. The non-adiabatic couplings between adsorbate and surface are computed perturbatively, for which our recently introduced state-resolved anharmonic rate model is used. It is shown that mode- and state-selective excitation can be achieved in the absence of dissipation when using optimized laser pulses. The inclusion of dissipation in the model reduces the state selectivity and the population transfer yield to highly excited states. In this case, mode activation is most effectively realized by a rational pulse of carefully chosen duration rather than by a locally optimized pulse. KW - dissipative dynamics KW - photochemistry KW - quantum control KW - surface chemistry Y1 - 2012 U6 - https://doi.org/10.1002/ijch.201100097 SN - 0021-2148 VL - 52 IS - 5 SP - 438 EP - 451 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Andrianov, Igor V. A1 - Klamroth, Tillmann A1 - Saalfrank, Peter A1 - Bovensiepen, U. A1 - Gahl, Cornelius A1 - Wolf, M. M. T1 - Quantum theoretical study of electron solvation dynamics in ice layers on a Cu(111) surface N2 - Recent experiments using time- and angle-resolved two-photon photoemission (2PPE) spectroscopy at metal/polar adsorbate interfaces succeeded in time-dependent analysis of the process of electron solvation. A fully quantum mechanical, two-dimensional simulation of this process, which explicitly includes laser excitation, is presented here, confirming the origin of characteristic features, such as the experimental observation of an apparently negative dispersion. The inference of the spatial extent of the localized electron states from the angular dependence of the 2PPE spectra has been found to be non-trivial and system-dependent. (C) 2005 American Institute of Physics Y1 - 2005 SN - 0021-9606 ER - TY - THES A1 - Klamroth, Tillmann T1 - Quantum mechanical simulations for correlated many-electron dynamics and electron induced processes at surfaces Y1 - 2006 CY - Potsdam ER - TY - JOUR A1 - Paramonov, Guennaddi K. A1 - Klamroth, Tillmann A1 - Lu, H. Z. A1 - Bandrauk, Andre D. T1 - Quantum dynamics, isotope effects, and power spectra of H-2(+) and HD+ excited to the continuum by strong one-cycle laser pulses: Three-dimensional non-Born-Oppenheimer simulations JF - Physical review : A, Atomic, molecular, and optical physics N2 - Non-Born-Oppenheimer quantum dynamics of H-2(+) and HD+ excited by single one-cycle laser pulses linearly polarized along the molecular (z) axis have been studied within a three-dimensional model, including the internuclear distance R and electron coordinates z and rho, by means of the numerical solution of the time-dependent Schrodinger equation on the timescale of about 200 fs. Laser carrier frequencies corresponding to the wavelengths of lambda(l) = 400 and 50 nm have been used and the amplitudes of the pulses have been chosen such that the energies of H-2(+) and HD+ are above the dissociation threshold after the ends of the laser pulses. It is shown that excitation of H-2(+) and HD+ above the dissociation threshold is accompanied by formation of vibrationally "hot" and "cold" ensembles of molecules. Dissociation of vibrationally "hot" molecules does not prevent the appearance of post-laser-pulse electronic oscillations, parallel z oscillations, and transversal rho oscillations. Moreover, dissociation of "hot" molecules does not influence characteristic frequencies of electronic z and rho oscillations. The main difference between the laser-induced quantum dynamics of homonuclear H-2(+) and its heteronuclear isotope HD+ is that fast post-laser-pulse electronic z oscillations in H-2(+) are regularly shaped with the period of tau(shp) approximate to 30 fs corresponding to nuclear oscillations in H-2(+), while electronic z oscillations in HD+ arise as "echo pulses" of its initial excitation and appear with the period of tau(echo) approximate to 80 fs corresponding to nuclear motion in HD+. Accordingly, corresponding power spectra of nuclear motion contain strong low-frequency harmonics at omega(shp) = 2 pi/tau(shp) in H2(+) and omega(echo) = 2 pi/tau(echo) in HD+. Power spectra related to both electronic and nuclear motion have been calculated in the acceleration form. Both higher- and lower-order harmonics are generated at the laser wavelength lambda(l) = 400 nm, while only lower-order harmonics are well pronounced at lambda(l) = 50 nm. It is also shown that a rationalized harmonic order, defined in terms of the frequency of the laser-induced electronic z oscillations, agrees with the concept of inversion symmetry for electronic motion in diatomic molecules. Y1 - 2018 U6 - https://doi.org/10.1103/PhysRevA.98.063431 SN - 2469-9926 SN - 2469-9934 VL - 98 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Saalfrank, Peter A1 - Nest, Mathias A1 - Andrianov, Igor V. A1 - Klamroth, Tillmann A1 - Kroner, Dominic A1 - Beyvers, Stephanie T1 - Quantum dynamics of laser-induced desorption from metal and semiconductor surfaces, and related phenomena N2 - Recent progress towards a quantum theory of laser-induced desorption and related phenomena is reviewed, for specific examples. These comprise the photodesorption of NO from Pt(111), the scanning tunnelling microscope and laser- induced desorption and switching of H at Si(100), and the electron stimulated desorption and dissociation of CO at Ru(0001). The theoretical methods used for nuclear dynamics range from open-system density matrix theory over nonadiabatically coupled multi-state models to electron-nuclear wavepackets. Also, aspects of time-dependent spectroscopy to probe ultrafast nonadiabatic processes at surfaces will be considered for the example of two-photon photoemission of solvated electrons in ice layers on Cu(111) Y1 - 2006 UR - http://iopscience.iop.org/0953-8984/18/30/S05/pdf/0953-8984_18_30_S05.pdf U6 - https://doi.org/10.1088/0953-8984/18/30/S05 SN - 1361-648X SN - 0953-8984 VL - 18 IS - 30 SP - S1425 EP - S1459 PB - IOP Publ. CY - Bristol ER - TY - JOUR A1 - Füchsel, Gernot A1 - Tremblay, Jean Christophe A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Quantum dynamical simulations of the femtosecond-laser-induced ultrafast desorption of H2 and D2 from Ru(0001) JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - We investigate the recombinative desorption of hydrogen and deuterium from a Ru(0001) surface initiated by femtosecond laser pulses. We adopt a quantum mechanical two-state model including three molecular degrees of freedom to describe the dynamics within the desorption induced by electronic transition (DIET) limit. The energy distributions as well as the state-resolved and ensemble properties of the desorbed molecules are analyzed in detail by using the time-energy method. Our results shed light on the experimentally observed 1) large isotopic effects regarding desorption yields and translational energies and 2) the nonequal energy partitioning into internal and translational modes. In particular, it is shown that a single temperature is sufficient to characterize the energy distributions for all degrees of freedom. Further, we confirm that quantization effects play an important role in the determination of the energy partitioning. KW - quantum dynamics KW - laser chemistry KW - isotope effects KW - surface chemistry KW - ultrafast reactions Y1 - 2013 U6 - https://doi.org/10.1002/cphc.201200940 SN - 1439-4235 VL - 14 IS - 7 SP - 1471 EP - 1478 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Pan, Tianluo A1 - Klamroth, Tillmann A1 - Palmer, Richard E. T1 - Quantum chemical cluster models for chemi- and physisorption of chlorobenzene on Si(111)-7x7 JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - Motivated by recent atomic manipulation experiments, we report quantum chemical calculations for chemi- and physisorption minima of chlorobenzene on the Si(111)-7x7 surface. A density functional theory cluster approach is applied, using the B3LYP hybrid functional alongside Grimme's empirical dispersion corrections (D3). We were able to identify chemisorption sites of binding energies of 1.6 eV and physisorption energies of 0.6 eV, both in encouraging agreement with the trend of experimental data. The cluster approach opens up the possibility of a first-principles based dynamical description of STM manipulation experiments on this system, the interpretation of which involves both the chemi- and physisorbed states. However, we found that special care has to be taken regarding the choice of clusters, basis sets, and the evaluation of the dispersion corrections. Y1 - 2014 U6 - https://doi.org/10.1021/jp504208d SN - 1089-5639 VL - 118 IS - 33 SP - 6699 EP - 6704 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Palmer, Richard E. A1 - Klamroth, Tillmann T1 - Quantum chemical approach to atomic manipulation of chlorobenzene on the Si(111)-7 x 7 surface BT - Resonance localization, vibrational activation, and surface dynamics JF - Physical review materials N2 - We present a cluster model to describe the localization of hot charge carriers on the Si(111)-7 x 7 surface, which leads to (nonlocal) desorption of chlorobenzene molecules in scanning tunneling microscope (STM) manipulation experiments. The localized charge carriers are modeled by a small cluster. By means of quantum chemical calculations, this cluster model explains many experimental findings from STM manipulation. We show that the negative charge is mainly localized in the surface, while the positive one also resides on the molecule. Both resonances boost desorption: In the negative resonance the adatom is elevated; in the positive one the chemisorption bond between the silicon surface adatom and chlorobenzene is broken. We find normal modes promoting desorption matching experimental low-temperature activation energies for electron-and hole-induced desorption. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevMaterials.1.026001 SN - 2475-9953 VL - 1 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Ehlert, Christopher A1 - Klamroth, Tillmann T1 - PSIXAS: A Psi4 plugin for efficient simulations of X-ray absorption spectra based on the transition-potential and Delta-Kohn-Sham method JF - Journal of computational chemistry : organic, inorganic, physical, biological N2 - Near edge X-ray absorption fine structure (NEXAFS) spectra and their pump-probe extension (PP-NEXAFS) offer insights into valence- and core-excited states. We present PSIXAS, a recent implementation for simulating NEXAFS and PP-NEXAFS spectra by means of the transition-potential and the Delta-Kohn-Sham method. The approach is implemented in form of a software plugin for the Psi4 code, which provides access to a wide selection of basis sets as well as density functionals. We briefly outline the theoretical foundation and the key aspects of the plugin. Then, we use the plugin to simulate PP-NEXAFS spectra of thymine, a system already investigated by others and us. It is found that larger, extended basis sets are needed to obtain more accurate absolute resonance positions. We further demonstrate that, in contrast to ordinary NEXAFS simulations, where the choice of the density functional plays a minor role for the shape of the spectrum, for PP-NEXAFS simulations the choice of the density functional is important. Especially hybrid functionals (which could not be used straightforwardly before to simulate PP-NEXAFS spectra) and their amount of "Hartree-Fock like" exact exchange affects relative resonance positions in the spectrum. KW - transition-potential method KW - X-ray absorption KW - spectroscopy KW - Delta-Kohn-Sham Y1 - 2020 U6 - https://doi.org/10.1002/jcc.26219 SN - 0192-8651 SN - 1096-987X VL - 41 IS - 19 SP - 1781 EP - 1789 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Klamroth, Tillmann T1 - Optimal control of ultrafast laser driven many-electron dynamics in a polyatomic molecule: N-methyl-6-quinolone N2 - We report time-dependent configuration interaction singles calculations for the ultrafast laser driven many- electron dynamics in a polyatomic molecule, N-methyl-6-quinolone. We employ optimal control theory to achieve a nearly state-selective excitation from the S-0 to the S-1 state, on a time scale of a few (approximate to 6) femtoseconds. The optimal control scheme is shown to correct for effects opposing a state-selective transition, such as multiphoton transitions and other, nonlinear phenomena, which are induced by the ultrashort and intense laser fields. In contrast, simple two-level pi pulses are not effective in state-selective excitations when very short pulses are used. Also, the dependence of multiphoton and nonlinear effects on the number of states included in the dynamical simulations is investigated. Y1 - 2006 UR - http://jcp.aip.org/ U6 - https://doi.org/10.1063/1.2185633 SN - 0021-9606 ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers a study based on density functional theory JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Based on the analysis of optical absorption spectra, it has recently been speculated that the excitonic coupling between individual azobenzene-functionalized alkanethiols arranged in a self-assembled monolayer (SAM) on a gold surface could be strong enough to hinder collective trans-cis isomerization-on top of steric hindrance [Gahl et al., J. Am. Chem. Soc., 2010, 132, 1831]. Using models of SAMs of increasing complexity (dimer, linear N-mers, and two-dimensionally arranged N-mers) and density functional theory on the (TD-) B3LYP/6-31G* level, we determine optical absorption spectra, the nature and magnitude of excitonic couplings, and the corresponding spectral shifts. It is found that at inter-monomer distances of about 20 angstrom and above, TD-B3LYP excitation frequencies (and signal intensities) can be well described by the frequently used point-dipole approximation. Further, calculated blue shifts in optical absorption spectra account for the experimental observations made for azobenzene/gold SAMs, and hint to the fact that they can indeed be responsible for reduced switching probability in densely packed self-assembled structures. Y1 - 2011 U6 - https://doi.org/10.1039/c1cp22793a SN - 1463-9076 VL - 13 IS - 48 SP - 21608 EP - 21614 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Thiel, Kerstin A1 - Klamroth, Tillmann A1 - Strauch, Peter A1 - Taubert, Andreas T1 - On the interaction of ascorbic acid and the tetrachlorocuprate ion [CuCl4](2-) in CuCl nanoplatelet formation from an ionic liquid precursor (ILP) JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - The formation of CuCl nanoplatelets from the ionic liquid precursor (ILP) butylpyridinium tetrachlorocuprate [C4Py](2)[CuCl4] using ascorbic acid as a reducing agent was investigated. In particular, electron paramagnetic resonance (EPR) spectroscopy was used to evaluate the interaction between ascorbic acid and the Cu(II) ion before reduction to Cu(I). EPR spectroscopy suggests that the [CuCl4](2-) ion in the neat IL is a distorted tetrahedron, consistent with DFT calculations. Addition of ascorbic acid leads to the removal of one chloride from the [CuCl4](2-) anion, as shown by DFT and the loss of symmetry by EPR. DFT furthermore suggests that the most stable adduct is formed when only one hydroxyl group of the ascorbic acid coordinates to the Cu(II) ion. Y1 - 2011 U6 - https://doi.org/10.1039/c1cp20648f SN - 1463-9076 VL - 13 IS - 30 SP - 13537 EP - 13543 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Füchsel, Gernot A1 - Klamroth, Tillmann A1 - Dokic, Jadranka A1 - Saalfrank, Peter T1 - On the electronic structure of neutral and ionic azobenzenes and their possible role as surface mounted molecular switches JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - We report quantum chemical calculations, mostly based on density functional theory, on azobenzene and substituted azobenzenes as neutral molecules or ions, in ground and excited states. Both the cis and trans configurations are computed as well as the activation energies to transform one isomer into the other and the possible reaction paths and reaction surfaces along the torsion and inversion modes. All calculations are done for the isolated species, but results are discussed in light of recent experiments aiming at the switching of surface mounted azobenzenes by scanning tunneling microscopes. Y1 - 2006 U6 - https://doi.org/10.1021/jp060969v SN - 1520-6106 VL - 110 IS - 33 SP - 16337 EP - 16345 PB - Soc. CY - Washington ER - TY - JOUR A1 - Gaebel, Tina A1 - Bein, Daniel A1 - Mathauer, Daniel A1 - Utecht, Manuel A1 - Palmer, Richard E. A1 - Klamroth, Tillmann T1 - Nonlocal STM manipulation of chlorobenzene on Si(111)-7 x 7 BT - Potentials, kinetics, and first-principles molecular dynamics calculations for open systems JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - We use quantum chemical cluster models together with constrained density STM Ph CI functional theory (DFT) and ab initio molecular dynamics (AIMD) for open system to simulate tip and rationalize nonlocal scanning tunneling microscope (STM) manipulation experiments for Philh ci chlorobenzene (PhCl) on a Si(111)-7 X 7 surface. We consider three different processes, namely, the electron-induced dissociation of the carbon-chlorine bond for physisorbed PhCl molecules at low temperatures and the electron- or hole-induced desorption of chemisorbed PhCl at 300 K. All processes can be induced nonlocally, i.e., up to several nanometers (nm) away from the injection site, in STM experiments. We rationalize and explain the experimental findings regarding the STM-induced dissociation using constrained DFT. The coupling of STM-induced ion resonances to nuclear degrees of freedom is simulated with AIMD using the Gadzuk averaging approach for open systems. From this data, we predict a 4 fs lifetime for the cationic resonance. For the anion model, desorption could not be observed. In addition, the same cluster models are used for transition-state theory calculations, which are compared to and validated against time-lapse STM experiments. Y1 - 2021 U6 - https://doi.org/10.1021/acs.jpcc.1c02612 SN - 1932-7447 SN - 1932-7455 VL - 125 IS - 22 SP - 12175 EP - 12184 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schwarze, Thomas A1 - Kelling, Alexandra A1 - Müller, Holger A1 - Trautmann, Michael A1 - Klamroth, Tillmann A1 - Baumann, Otto A1 - Strauch, Peter A1 - Holdt, Hans-Jürgen T1 - N-2-Pyridinylmethyl-N '-arylmethyl-diaminomaleonitriles: New Highly Selective Chromogenic Chemodosimeters for Copper(II) JF - Chemistry - a European journal KW - amides KW - chemodosimeter KW - colorimetric detection KW - copper KW - sensors KW - UV KW - Vis spectroscopy Y1 - 2012 U6 - https://doi.org/10.1002/chem.201201731 SN - 0947-6539 VL - 18 IS - 34 SP - 10506 EP - 10510 PB - Wiley-VCH CY - Weinheim ER - TY - CHAP A1 - Saalfrank, Peter A1 - Bedurke, Florian A1 - Heide, Chiara A1 - Klamroth, Tillmann A1 - Klinkusch, Stefan A1 - Krause, Pascal A1 - Nest, Mathias A1 - Tremblay, Jean Christophe ED - Ruud, Kenneth ED - Brändas, Erkki J. T1 - Molecular attochemistry: correlated electron dynamics driven by light T2 - Advances in quantum chemistry N2 - Modern laser technology and ultrafast spectroscopies have pushed the timescales for detecting and manipulating dynamical processes in molecules from the picosecond over femtosecond domains, to the attosecond regime (1 as = 10(-18) s). This way, real-time dynamics of electrons after their photoexcitation can be probed and manipulated. In particular, experiments are moving more and more from atomic and solid state systems to molecules, opening the fields of "molecular electron dynamics" and "attosecond chemistry." Also on the theory side, powerful quantum dynamical tools have been developed to rationalize experiments on ultrafast electron dynamics in molecular species.
In this contribution, we concentrate on theoretical aspects of ultrafast electron dynamics in molecules, mostly driven by lasers. The dynamics will be described with the help of wavefunction-based ab initio methods such as time-dependent configuration interaction (TD-CI) or the multiconfigurational time-dependent Hartree-Fock (MCTDHF) methods. Besides a survey of the methods and their extensions toward, e.g., treatment of ionization, laser pulse optimization, and open quantum systems, two specific examples of applications will be considered: The creation and/or dynamical fate of electronic wavepackets, and the nonlinear optical response to laser pulse excitation in molecules by high harmonic generation (HHG). KW - dipole approximation KW - electron dynamics KW - electronic wavepackets KW - high harmonic generation KW - ionization KW - optimal control theory KW - time-dependent Schrödinger equation Y1 - 2020 SN - 978-0-12-819757-8 U6 - https://doi.org/10.1016/bs.aiq.2020.03.001 SN - 0065-3276 VL - 81 SP - 15 EP - 50 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Malic, E. A1 - Weber, C. A1 - Richter, M. A1 - Atalla, V. A1 - Klamroth, Tillmann A1 - Saalfrank, Peter A1 - Reich, Sebastian A1 - Knorr, A. T1 - Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches JF - Physical review letters N2 - The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.106.097401 SN - 0031-9007 VL - 106 IS - 9 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Bedurke, Florian A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Many-electron dynamics in laser-driven molecules BT - wavefunction theory vs. density functional theory JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - With recent experimental advances in laser-driven electron dynamics in polyatomic molecules, the need arises for their reliable theoretical modelling. Among efficient, yet fairly accurate methods for many-electron dynamics are Time-Dependent Configuration Interaction Singles (TD-CIS) (a Wave Function Theory (WFT) method), and Real-Time Time-Dependent Density Functional Theory (RT-TD-DFT), respectively. Here we compare TD-CIS combined with extended Atomic Orbital (AO) bases, TD-CIS/AO, with RT-TD-DFT in a grid representation of the Kohn-Sham orbitals, RT-TD-DFT/Grid. Possible ionization losses are treated by complex absorbing potentials in energy space (for TD-CIS/AO) or real space (for RT-TD-DFT), respectively. The comparison is made for two test cases: (i) state-to-state transitions using resonant lasers (pi-pulses), i.e., bound electron motion, and (ii) large-amplitude electron motion leading to High Harmonic Generation (HHG). Test systems are a H-2 molecule and cis- and trans-1,2-dichlorethene, C2H2Cl2, (DCE). From time-dependent electronic energies, dipole moments and from HHG spectra, the following observations are made: first, for bound state-to-state transitions enforced by pi-pulses, TD-CIS nicely accounts for the expected population inversion in contrast to RT-TD-DFT, in agreement with earlier findings. Secondly, when using laser pulses under non-resonant conditions, dipole moments and lower harmonics in HHG spectra are obtained by TD-CIS/AO which are in good agreement with those obtained with RT-TD-DFT/Grid. Deviations become larger for higher harmonics and at low laser intensities, i.e., for low-intensity HHG signals. We also carefully test effects of basis sets for TD-CIS/AO and grid size for RT-TD-DFT/Grid, different exchange-correlation functionals in RT-TD-DFT, and absorbing boundaries. Finally, for the present examples, TD-CIS/AO is observed to be at least an order of magnitude more computationally efficient than RT-TD-DFT/Grid. Y1 - 2021 U6 - https://doi.org/10.1039/d1cp01100f SN - 1463-9076 SN - 1463-9084 VL - 23 IS - 24 SP - 13544 EP - 13560 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schwarze, Thomas A1 - Mueller, Holger A1 - Dosche, Carsten A1 - Klamroth, Tillmann A1 - Mickler, Wulfhard A1 - Kelling, Alexandra T1 - Luminescence detection of open-shell transition-metal ions by photoinduced electron transfer controlled by internal charge transfer of a receptor Y1 - 2007 UR - http://onlinelibrary.wiley.com/doi/10.1002/ange.200603992/pdf U6 - https://doi.org/10.1002/anie.200603992 ER - TY - JOUR A1 - Klinkusch, Stefan A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Long-range intermolecular charge transfer induced by laser pulses : an explicitly time-dependent configuration interaction approach N2 - In this paper, we report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (TD-CIS) approach. The method is capable of describing explicitly time-dependent phenomena beyond perturbation theory and is systematically improvable. In contrast to most time-dependent density functional methods it also allows us to treat long-range charge-transfer states properly. As an example, the laser-pulse induced charge transfer between a donor (ethylene) and an acceptor molecule (tetracyanoethylene, TCNE) is studied by means of TD-CIS. Also, larger aggregates consisting of several donors and/or acceptors are considered. It is shown that the charge distribution and hence the dipole moments of the systems under study are switchable by (a series of) laser pulses which induce selective, state-to-state electronic transitions. Y1 - 2009 UR - http://xlink.rsc.org/jumptojournal.cfm?journal_code=CP U6 - https://doi.org/10.1039/B817873a SN - 1463-9076 ER - TY - GEN A1 - Utecht, Manuel Martin A1 - Klamroth, Tillmann T1 - Local resonances in STM manipulation of chlorobenzene on Si(111)-7×7 BT - performance of different cluster models and density functionals T2 - Molecular Physics N2 - Hot localised charge carriers on the Si(111)-7×7 surface are modelled by small charged clusters. Such resonances induce non-local desorption, i.e. more than 10 nm away from the injection site, of chlorobenzene in scanning tunnelling microscope experiments. We used such a cluster model to characterise resonance localisation and vibrational activation for positive and negative resonances recently. In this work, we investigate to which extent the model depends on details of the used cluster or quantum chemistry methods and try to identify the smallest possible cluster suitable for a description of the neutral surface and the ion resonances. Furthermore, a detailed analysis for different chemisorption orientations is performed. While some properties, as estimates of the resonance energy or absolute values for atomic changes, show such a dependency, the main findings are very robust with respect to changes in the model and/or the chemisorption geometry. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 463 KW - DFT KW - cluster model KW - charge localisation KW - STM Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-412970 ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Klamroth, Tillmann T1 - Local resonances in STM manipulation of chlorobenzene on Si(111)-7x7 BT - performance of different cluster models and density functionals JF - Molecular physics N2 - Hot localised charge carriers on the Si(111)-7x7 surface are modelled by small charged clusters. Such resonances induce non-local desorption, i.e. more than 10 nm away from the injection site, of chlorobenzene in scanning tunnelling microscope experiments. We used such a cluster model to characterise resonance localisation and vibrational activation for positive and negative resonances recently. In this work, we investigate to which extent the model depends on details of the used cluster or quantum chemistry methods and try to identify the smallest possible cluster suitable for a description of the neutral surface and the ion resonances. Furthermore, a detailed analysis for different chemisorption orientations is performed. While some properties, as estimates of the resonance energy or absolute values for atomic changes, show such a dependency, the main findings are very robust with respect to changes in the model and/or the chemisorption geometry. [GRAPHICS] . KW - DFT KW - cluster model KW - charge localisation KW - STM Y1 - 2018 U6 - https://doi.org/10.1080/00268976.2018.1442939 SN - 0026-8976 SN - 1362-3028 VL - 116 IS - 13 SP - 1687 EP - 1696 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Klinkusch, Stefan A1 - Saalfrank, Peter A1 - Klamroth, Tillmann T1 - Laser-induced electron dynamics including photoionization : a heuristic model within time-dependent configuration interaction theory N2 - We report simulations of laser-pulse driven many-electron dynamics by means of a simple, heuristic extension of the time-dependent configuration interaction singles (TD-CIS) approach. The extension allows for the treatment of ionizing states as nonstationary states with a finite, energy-dependent lifetime to account for above-threshold ionization losses in laser-driven many-electron dynamics. The extended TD-CIS method is applied to the following specific examples: (i) state-to-state transitions in the LiCN molecule which correspond to intramolecular charge transfer, (ii) creation of electronic wave packets in LiCN including wave packet analysis by pump-probe spectroscopy, and, finally, (iii) the effect of ionization on the dynamic polarizability of H-2 when calculated nonperturbatively by TD-CIS. Y1 - 2009 UR - http://jcp.aip.org/ U6 - https://doi.org/10.1063/1.3218847 SN - 0021-9606 ER - TY - JOUR A1 - Klamroth, Tillmann T1 - Laser-driven electron transfer through metal-insulator-metal contacts : time-dependent configuration interaction singles calculations for a jellium model N2 - In this paper we report time-dependent configuration interaction singles calculations modeling the laser- induced current through a metal-insulator-metal (MIM) contact. We compare our results to recent experiments [D. Diesing, M. Merschdorf, A. Thon, and W. Pfeiffer, Appl. Phys. B (to be published)]. We use two jellium slabs separated by a vacuum region in a one-dimensional model to describe the MIM contact. The contact is coupled to ultrashort (fs) laser pulses by the semiclassical dipole approximation. We discuss simulated two-pulse correlation spectra in comparison to experimental results Y1 - 2003 SN - 1098-0121 ER - TY - JOUR A1 - Saalfrank, Peter A1 - Klamroth, Tillmann A1 - Huber, C. A1 - Krause, Pascal T1 - Laser-driven electron dynamics at interfaces N2 - In this paper we present time-dependent, quantum-dynamical simulations of photoinduced processes at solid surfaces involving nonadiabatic transitions of electrons to and from short-lived intermediate excited states. In particular, two-photon photoemission (2PPE) spectra of naked metal surfaces and free-standing metal films are considered. One major problem in both cases is the presence of electron-electron scattering, which is treated here in various ways. The first way is to adopt an open-system density matrix approach, in which a single electron is weakly coupled to a "bath" of other electrons. The second approach is based on a many-electron Schrodinger equation, which is solved with the help of a time-dependent configuration interactions singles (TD-CIS) method Y1 - 2005 SN - 0021-2148 ER - TY - JOUR A1 - Klamroth, Tillmann A1 - Kroner, Dominic A1 - Saalfrank, Peter T1 - Laser-driven coupled electron-nuclear dynamics : Quantum mechanical simulation of molecular photodesorption from metal films N2 - In this paper we report dynamical simulations of laser-driven, coupled nuclear-electron dynamics for a molecule- surface system. Specifically, the laser desorption of a small molecule (NO) from a metal slab (Pt) in the so-called DIET limit (Desorption Induced by Electronic Transitions), is studied. The excitation of the metal electrons by a laser pulse followed by the formation of a negative ion resonance, its subsequent decay, and the simultaneous desorption of the molecule are all treated within a single quantum mechanical model. This model is based on an earlier theory of Harris and others [S. M. Harris, S. Holloway, and G. R. Darling, J. Chem. Phys. 102, 8235 (1995)], according to which a nuclear degree of freedom is coupled to an electronic one, both propagated on a single non-Born-Oppenheimer potential energy surface. The goals of the present contribution are (i) to make a conceptual connection of this model to the frequently adopted nonadiabatic "multi-state" models of photodesorption, (ii) to understand details of the desorption mechanism, (iii) to explicitly account for the laser pulse, and (iv) to study the photodesorption as a function of the thickness of the metal film, and the laser parameters. As an important methodological aspect we also present a highly efficient numerical scheme to propagate the wave packet in a problem-adapted diabatic basis Y1 - 2005 SN - 1098-0121 ER - TY - JOUR A1 - Floss, Gereon A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Laser-controlled switching of molecular arrays in an dissipative environment JF - Physical review : B, Condensed matter and materials physics N2 - The optical switching of molecular ensembles in a dissipative environment is a subject of various fields of chemical physics and physical chemistry. Here we try to switch arrays of molecules from a stable collective ground state to a state in which all molecules have been transferred to another stable higher-energy configuration. In our model switching proceeds through electronically excited intermediates which are coherently coupled to each other through dipolar interactions, and which decay incoherently within a finite lifetime by coupling to a dissipative environment. The model is quite general, but parameters are chosen to roughly resemble the all-trans -> all-cis isomerization of an array of azobenzene molecules on a surface. Using analytical and optimal control pulses and the concept of "laser distillation," we demonstrate that for various aggregates (dimers up to hexamers), controlled and complete switching should be possible. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevB.83.104301 SN - 1098-0121 VL - 83 IS - 10 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kroener, Dominik A1 - Schimka, Selina A1 - Klamroth, Tillmann T1 - Laser control for coupled torsions in chiroptical switches: a combined quantum and classical dynamics approach JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - We present a novel laser pulse control for the chiroptical switch 1-(2-cis-fluoroethenyl)-2-fluoro-3,5-dibromobenzene mounted on adamantane, where the latter imitates a linker group or part of a solid surface. This molecular device offers three switching states: a true achiral "off"-state and two chiral "on"-states of opposite handedness. Due to the alignment of its chiral axis along the surface normal several defined orientations of the switch have to be considered for an efficient stereocontrol strategy. In addition to these different initial conditions, coupled torsional degrees of freedom around the chiral axis make the quest for highly stereoselective laser pulses a challenge. The necessary flexibility in pulse accomplished by employing the iterative stochastic pulse optimization method we presented recently. Still, the complexity of the system dictates a combined treatment by fast molecular dynamics and computationally intensive quantum dynamics. Although quantum effects are found to be of importance, the pulses optimized within the classical treatment allow us to turn on the chirality of the switch, achieving high enantioselectivity in the quantum treatment for all orientations at the same time. Y1 - 2014 U6 - https://doi.org/10.1021/jp410342a SN - 1932-7447 VL - 118 IS - 2 SP - 1322 EP - 1331 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kraus, Florian A1 - Aschenbrenner, Jürgen C. A1 - Klamroth, Tillmann A1 - Korber, Nikolaus T1 - Hydrogen polyphosphides P3H23- and P3H32- : synthesis and crystal structure of K3(P3H2)·2.3NH3, Rb3(P3H2)·NH3, [Rb(18-crown-6)]2(P3H3)·7.5NH3, and [Cs(18-crown-6)]2(P3H3)·7NH3 N2 - The incongruous solvation of polyphosphides and phosphanes or the direct reduction of white phosphorus in liquid ammonia leads to the hydrogen polyphosphides catena-dihydrogen triphosphide, P3H23-, and catena-trihydrogen triphosphide, P3H32-, in the crystalline compounds K-3(P3H2)center dot 2.3NH(3) (1), Rb-3(P3H2)center dot NH3 (2), [Rb(18-crown-6)](2)(P3H3)center dot 7.5NH(3) (3), and [Cs(18-crown-6)](2)(P3H3)center dot 7NH(3) (4). Y1 - 2009 UR - http://pubs.acs.org/journal/inocaj U6 - https://doi.org/10.1021/Ic8014546 SN - 0020-1669 ER - TY - JOUR A1 - Ast, Sandra A1 - Müller, Holger A1 - Flehr, Roman A1 - Klamroth, Tillmann A1 - Walz, Bernd A1 - Holdt, Hans-Jürgen T1 - High Na+ and K+-induced fluorescence enhancement of a pi-conjugated phenylaza-18-crown-6-triazol-substituted coumarin fluoroionophore JF - Chemical communications N2 - The new pi-conjugated 1,2,3-triazol-1,4-diyl fluoroionophore 1 generated via Cu(I) catalyzed [3 + 2] cycloaddition shows high fluorescence enhancement factors (FEF) in the presence of Na+ (FEF = 58) and K+ (FEF = 27) in MeCN and high selectivity towards K+ under simulated physiological conditions (160 mM K+ or Na+, respectively) with a FEF of 2.5 for K+. Y1 - 2011 U6 - https://doi.org/10.1039/c0cc04370b SN - 1359-7345 VL - 47 IS - 16 SP - 4685 EP - 4687 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Witzorky, Christoph A1 - Paramonov, Guennaddi A1 - Bouakline, Foudhil A1 - Jaquet, Ralph A1 - Saalfrank, Peter A1 - Klamroth, Tillmann T1 - Gaussian-type orbital calculations for high harmonic generation in vibrating molecules BT - Benchmarks for H-2(+) JF - Journal of chemical theory and computation N2 - The response of the hydrogen molecular ion, H-2(+), to few-cycle laser pulses of different intensities is simulated. To treat the coupled electron-nuclear motion, we use adiabatic potentials computed with Gaussian-type basis sets together with a heuristic ionization model for the electron and a grid representation for the nuclei. Using this mixed-basis approach, the time-dependent Schrodinger equation is solved, either within the Born-Oppenheimer approximation or with nonadiabatic couplings included. The dipole response spectra are compared to all-grid-based solutions for the three-body problem, which we take as a reference to benchmark the Gaussian-type basis set approaches. Also, calculations employing the fixed-nuclei approximation are performed, to quantify effects due to nuclear motion. For low intensities and small ionization probabilities, we get excellent agreement of the dynamics using Gaussian-type basis sets with the all-grid solutions. Our investigations suggest that high harmonic generation (HHG) and high-frequency response, in general, can be reliably modeled using Gaussian-type basis sets for the electrons for not too high harmonics. Further, nuclear motion destroys electronic coherences in the response spectra even on the time scale of about 30 fs and affects HHG intensities, which reflect the electron dynamics occurring on the attosecond time scale. For the present system, non-Born-Oppenheimer effects are small. The Gaussian-based, nonadiabatically coupled, time-dependent multisurface approach to treat quantum electron-nuclear motion beyond the non-Born-Oppenheimer approximation can be easily extended to approximate wavefunction methods, such as time-dependent configuration interaction singles (TD-CIS), for systems where no benchmarks are available. KW - Basis sets KW - Chemical calculations KW - Ionization KW - Lasers KW - Quantum mechanics Y1 - 2021 U6 - https://doi.org/10.1021/acs.jctc.1c00837 SN - 1549-9618 SN - 1549-9626 VL - 17 IS - 12 SP - 7353 EP - 7365 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Vazhappilly, Tijo A1 - Klamroth, Tillmann A1 - Saalfrank, Peter A1 - Hernandez, Rigoberto T1 - Femtosecond-laser desorption of H-2 (D-2) from Ru(0001) : quantum and classical approaches N2 - The femtosecond-laser-induced, substrate-mediated associative desorption of molecular hydrogen and deuterium from a Ru(0001) surface in the so-called DIMET limit is studied theoretically. Two widely used models, a "quantum nonadiabatic" approach and a "classical adiabatic" one are employed and compared to each other. The quantum model is realized by the Monte Carlo wave packet (MCWP) method in the framework of open-system density matrix theory: The classical approach is realized with the help of (frictional) Langevin dynamics with stochastic forces. For both models the same ground-state potential energy surface is used and the same two-temperature model adopted to describe the hot- electron-driven desorption dynamics. Apart from these common features both models are different. Still, both account well for the main experimental findings (Wagner et al. Phys. Rev. B 2005, 72, 205404). In particular, an isotope effect in desorption probabilities, the energy content of the desorbing molecules, and the scaling of these observables with laser fluence are reproduced and explained. The similarity of the results obtained with both models is traced back to the fact that, in the present case, the photodynamics takes place dominantly in the ground electronic state because the electronically excited state is rapidly quenched. The short lifetime of the excited state has also the effect that photoreaction cross sections are typically very small. An IR+vis hybrid scheme, by which the adsorbate is vibrationally excited by IR photons prior to the heating of metal electrons with the vis pulse, is shown to successfully promote the reaction even for strongly coupled adsorbate-surface systems. Y1 - 2009 UR - http://pubs.acs.org/journal/jpccck U6 - https://doi.org/10.1021/Jp810709k SN - 1932-7447 ER - TY - JOUR A1 - Huber, Christian A1 - Klamroth, Tillmann T1 - Explicitly time-dependent coupled cluster singles doubles calculations of laser-driven many-electron dynamics JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - We report explicitly time-dependent coupled cluster singles doubles (TD-CCSD) calculations, which simulate the laser-driven correlated many-electron dynamics in molecular systems. Small molecules, i.e., HF, H(2)O, NH(3), and CH(4), are treated mostly with polarized valence double zeta basis sets. We determine the coupled cluster ground states by imaginary time propagation for these molecules. Excited state energies are obtained from the Fourier transform of the time-dependent dipole moment after an ultrashort, broadband laser excitation. The time-dependent expectation values are calculated from the complex cluster amplitudes using the corresponding configuration interaction singles doubles wave functions. Also resonant laser excitations of these excited states are simulated, in order to explore the limits for the numerical stability of our current TD-CCSD implementation, which uses time-independent molecular orbitals to form excited configurations. Y1 - 2011 U6 - https://doi.org/10.1063/1.3530807 SN - 0021-9606 VL - 134 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Bronner, C. A1 - Leyssner, F. A1 - Stremlau, S. A1 - Utecht, Manuel Martin A1 - Saalfrank, Peter A1 - Klamroth, Tillmann A1 - Tegeder, P. T1 - Electronic structure of a subnanometer wide bottom-up fabricated graphene nanoribbon: End states, band gap, and dispersion JF - Physical review : B, Condensed matter and materials physics N2 - Angle-resolved two-photon photoemission and high-resolution electron energy loss spectroscopy are employed to derive the electronic structure of a subnanometer atomically precise quasi-one-dimensional graphene nanoribbon (GNR) on Au(111). We resolved occupied and unoccupied electronic bands including their dispersion and determined the band gap, which possesses an unexpectedly large value of 5.1 eV. Supported by density functional theory calculations for the idealized infinite polymer and finite size oligomers, an unoccupied nondispersive electronic state with an energetic position in the middle of the band gap of the GNR could be identified. This state resides at both ends of the ribbon (end state) and is only found in the finite sized systems, i.e., the oligomers. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevB.86.085444 SN - 1098-0121 VL - 86 IS - 8 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Bronner, Christopher A1 - Utecht, Manuel Martin A1 - Haase, Anton A1 - Saalfrank, Peter A1 - Klamroth, Tillmann A1 - Tegeder, Petra T1 - Electronic structure changes during the surface-assisted formation of a graphene nanoribbon JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - High conductivity and a tunability of the band gap make quasi-one-dimensional graphene nanoribbons (GNRs) highly interesting materials for the use in field effect transistors. Especially bottom-up fabricated GNRs possess well-defined edges which is important for the electronic structure and accordingly the band gap. In this study we investigate the formation of a sub-nanometer wide armchair GNR generated on a Au(111) surface. The on-surface synthesis is thermally activated and involves an intermediate non-aromatic polymer in which the molecular precursor forms polyanthrylene chains. Employing angle-resolved two-photon photoemission in combination with density functional theory calculations we find that the polymer exhibits two dispersing states which we attribute to the valence and the conduction band, respectively. While the band gap of the non-aromatic polymer obtained in this way is relatively large, namely 5.25 +/- 0.06 eV, the gap of the corresponding aromatic GNR is strongly reduced which we attribute to the different degree of electron delocalization in the two systems. Y1 - 2014 U6 - https://doi.org/10.1063/1.4858855 SN - 0021-9606 SN - 1089-7690 VL - 140 IS - 2 PB - American Institute of Physics CY - Melville ER -