@article{ZenichowskiNacciFoelschetal.2012, author = {Zenichowski, Karl and Nacci, Ch and F{\"o}lsch, S. and Dokic, Jadranka and Klamroth, Tillmann and Saalfrank, Peter}, title = {STM-switching of organic molecules on semiconductor surfaces: an above threshold density matrix model for 1,5 cyclooctadiene on Si(100)}, series = {Journal of physics : Condensed matter}, volume = {24}, journal = {Journal of physics : Condensed matter}, number = {39}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-8984}, doi = {10.1088/0953-8984/24/39/394009}, pages = {11}, year = {2012}, abstract = {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.}, language = {en} } @article{ZenichowskiDokicKlamrothetal.2012, author = {Zenichowski, Karl and Dokic, Jadranka and Klamroth, Tillmann and Saalfrank, Peter}, title = {Current versus temperature-induced switching of a single molecule - open-system density matrix theory for 1,5-cyclooctadiene on Si(100)}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {136}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {9}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.3692229}, pages = {13}, year = {2012}, abstract = {The switching of single cyclooctadiene molecules chemisorbed on a Si(100) surface between two stable conformations, can be achieved with a scanning tunneling microscope [Nacci , Phys. Rev. B 77, 121405(R) (2008)]. Recently, it was shown by quantum chemical and quantum dynamical simulations that major experimental facts can be explained by a single-mode model with switching enforced by inelastic electron tunneling (IET) excitations and perturbed by vibrational relaxation [Nacci , Nano Lett. 9, 2997 (2009)]. In the present paper, we extend the previous theoretical work in several respects: (1) The model is generalized to a two-mode description in which two C2H4 units of COD can move independently; (2) contributions of dipole and, in addition, (cation and anion) resonance-IET rates are considered; (3) the harmonic-linear vibrational relaxation model used previously is generalized to anharmonic vibrations. While the present models highlight generic aspects of IET-switching between two potential minima, they also rationalize specific experimental findings for COD/Si(100): (1) A single-electron excitation mechanism with a linear dependence of the switching rate on tunneling current I, (2) the capability to switch both at negative and positive sample biases, and (3) a crossover temperature around similar to 60 K from an IET-driven, T-independent atom tunneling regime, to classical over-the-barrier isomerization with exponential T-dependence at higher temperatures for a bias voltage of +1.5 V and an average tunneling current of 0.73 nA.}, language = {en} } @article{WitzorkyParamonovBouaklineetal.2021, author = {Witzorky, Christoph and Paramonov, Guennaddi and Bouakline, Foudhil and Jaquet, Ralph and Saalfrank, Peter and Klamroth, Tillmann}, title = {Gaussian-type orbital calculations for high harmonic generation in vibrating molecules}, series = {Journal of chemical theory and computation}, volume = {17}, journal = {Journal of chemical theory and computation}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {1549-9618}, doi = {10.1021/acs.jctc.1c00837}, pages = {7353 -- 7365}, year = {2021}, abstract = {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.}, language = {en} } @article{WirthMonturetKlamrothetal.2011, author = {Wirth, Jonas and Monturet, Serge and Klamroth, Tillmann and Saalfrank, Peter}, title = {Adsorption and (photo-) electrochemical splitting of water on rutile ruthenium dioxide}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {93}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {6}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/93/68001}, pages = {6}, year = {2011}, abstract = {In this work, the adsorption and splitting of the water molecule by light and/or an external potential is investigated in the frame of (photo-) electrochemical cells using a rutile ruthenium dioxide anode. With the help of periodic density functional calculations, the adsorbed structures of H(2)O and some radicals involved in the splitting process (O, OH, OOH) are obtained and compared with the available experimental results. On the basis of these electronic-structure calculations, we use a method to calculate the stability of the reaction intermediates and conclude on the thermodynamical possibility of the water splitting reaction at the surface. We demonstrate that a moderate overpotential of 0.64 V is required for the reaction to take place at the RuO(2)(110) surface.}, language = {en} } @misc{WinterThielZabeletal.2013, author = {Winter, Alette and Thiel, Kerstin and Zabel, Andr{\´e} and Klamroth, Tillmann and P{\"o}ppl, Andreas and Kelling, Alexandra and Schilde, Uwe and Taubert, Andreas and Strauch, Peter}, title = {Tetrahalidocuprates(II) - structure and EPR spectroscopy}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-95012}, pages = {1019 -- 1030}, year = {2013}, abstract = {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.}, language = {en} } @article{WinterThielZabeletal.2014, author = {Winter, Alette and Thiel, Kerstin and Zabel, Andre and Klamroth, Tillmann and Poeppl, Andreas and Kelling, Alexandra and Schilde, Uwe and Taubert, Andreas and Strauch, Peter}, title = {Tetrahalidocuprates(II) - structure and EPR spectroscopy. Part 2: tetrachloridocuprates(II)}, series = {New journal of chemistry}, volume = {38}, journal = {New journal of chemistry}, number = {3}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1144-0546}, doi = {10.1039/c3nj01039b}, pages = {1019 -- 1030}, year = {2014}, abstract = {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.}, language = {en} } @article{VazhappillyKlamrothSaalfranketal.2009, author = {Vazhappilly, Tijo and Klamroth, Tillmann and Saalfrank, Peter and Hernandez, Rigoberto}, title = {Femtosecond-laser desorption of H-2 (D-2) from Ru(0001) : quantum and classical approaches}, issn = {1932-7447}, doi = {10.1021/Jp810709k}, year = {2009}, abstract = {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.}, language = {en} } @article{UtechtPanKlamrothetal.2014, author = {Utecht, Manuel Martin and Pan, Tianluo and Klamroth, Tillmann and Palmer, Richard E.}, title = {Quantum chemical cluster models for chemi- and physisorption of chlorobenzene on Si(111)-7x7}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {118}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {33}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/jp504208d}, pages = {6699 -- 6704}, year = {2014}, abstract = {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.}, language = {en} } @article{UtechtPalmerKlamroth2017, author = {Utecht, Manuel Martin and Palmer, Richard E. and Klamroth, Tillmann}, title = {Quantum chemical approach to atomic manipulation of chlorobenzene on the Si(111)-7 x 7 surface}, series = {Physical review materials}, volume = {1}, journal = {Physical review materials}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {2475-9953}, doi = {10.1103/PhysRevMaterials.1.026001}, pages = {5}, year = {2017}, abstract = {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.}, language = {en} } @article{UtechtKlamrothSaalfrank2011, author = {Utecht, Manuel Martin and Klamroth, Tillmann and Saalfrank, Peter}, title = {Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers a study based on density functional theory}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {48}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp22793a}, pages = {21608 -- 21614}, year = {2011}, abstract = {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.}, language = {en} } @article{UtechtKlamroth2018, author = {Utecht, Manuel Martin and Klamroth, Tillmann}, title = {Local resonances in STM manipulation of chlorobenzene on Si(111)-7x7}, series = {Molecular physics}, volume = {116}, journal = {Molecular physics}, number = {13}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0026-8976}, doi = {10.1080/00268976.2018.1442939}, pages = {1687 -- 1696}, year = {2018}, abstract = {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] .}, language = {en} } @misc{UtechtKlamroth2018, author = {Utecht, Manuel Martin and Klamroth, Tillmann}, title = {Local resonances in STM manipulation of chlorobenzene on Si(111)-7×7}, series = {Molecular Physics}, journal = {Molecular Physics}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-412970}, pages = {11}, year = {2018}, abstract = {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.}, language = {en} } @article{UtechtGaebelKlamroth2018, author = {Utecht, Manuel Martin and Gaebel, Tina and Klamroth, Tillmann}, title = {Desorption induced by low energy charge carriers on Si(111)-7 x 7}, series = {Journal of computational chemistry : organic, inorganic, physical, biological}, volume = {39}, journal = {Journal of computational chemistry : organic, inorganic, physical, biological}, number = {30}, publisher = {Wiley}, address = {Hoboken}, issn = {0192-8651}, doi = {10.1002/jcc.25607}, pages = {2517 -- 2525}, year = {2018}, abstract = {We use clusters for the modeling of local ion resonances caused by low energy charge carriers in STM-induced desorption of benzene derivates from Si(111)-7 x 7. We perform Born-Oppenheimer molecular dynamics for the charged systems assuming vertical transitions to the charged states at zero temperature, to rationalize the low temperature activation energies, which are found in experiment for chlorobenzene. Our calculations suggest very similar low temperature activation energies for toluene and benzene. For the cationic resonance transitions to physisorption are found even at 0 K, while the anion remains chemisorbed during the propagations. Further, we also extend our previous static quantum chemical investigations to toluene and benzene. In addition, an in depth analysis of the ionization potentials and electron affinities, which are used to estimate resonance energies, is given.}, language = {en} } @article{TraegerKlamrothKellingetal.2012, author = {Tr{\"a}ger, Juliane and Klamroth, Tillmann and Kelling, Alexandra and Lubahn, Susanne and Cleve, Ernst and Mickler, Wulfhard and Heydenreich, Matthias and M{\"u}ller, Holger and Holdt, Hans-J{\"u}rgen}, title = {Complexation of Palladium(II) with unsaturated Dithioethers a systematic development of highly selective ligands for solvent extraction}, series = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, journal = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, number = {14}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-1948}, doi = {10.1002/ejic.201101406}, pages = {2341 -- 2352}, year = {2012}, abstract = {There is a demand for new and robust PdII extractants due to growing recycling rates. Chelating dithioethers are promising substances for solvent extraction as they form stable square-planar complexes with PdII. We have modified unsaturated dithioethers, which are known to coordinate PdII, and adapted them to the requirements of industrial practice. The ligands are analogues of 1,2-dithioethene with varying electron-withdrawing backbones and polar end-groups. The crystal structures of several ligands and their palladium complexes were determined as well as their electro- and photochemical properties, complex stability and behaviour in solution. Solvent extraction experiments showed the superiority of some of our ligands over conventionally used extractants in terms of their very fast reaction rates. With highly selective 1,2-bis(2-methoxyethylthio)benzene (4) it is possible to extract PdII from a highly acidic medium in the presence of other base and palladium-group metals.}, language = {en} } @article{TremblayKrauseKlamrothetal.2010, author = {Tremblay, Jean Christophe and Krause, Pascal and Klamroth, Tillmann and Saalfrank, Peter}, title = {Time-dependent response of dissipative electron systems}, issn = {1050-2947}, doi = {10.1103/Physreva.81.063420}, year = {2010}, abstract = {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.}, language = {en} } @article{TremblayKlinkuschKlamrothetal.2011, author = {Tremblay, Jean Christophe and Klinkusch, Stefan and Klamroth, Tillmann and Saalfrank, Peter}, title = {Dissipative many-electron dynamics of ionizing systems}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {134}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.3532410}, pages = {10}, year = {2011}, abstract = {In this paper, we perform many-electron dynamics using the time-dependent configuration-interaction method in its reduced density matrix formulation (rho-TDCI). Dissipation is treated implicitly using the Lindblad formalism. To include the effect of ionization on the state-resolved dynamics, we extend a recently introduced heuristic model for ionizing states to the rho-TDCI method, which leads to a reduced density matrix evolution that is not norm-preserving. We apply the new method to the laser-driven excitation of H(2) in a strongly dissipative environment, for which the state-resolve lifetimes are tuned to a few femtoseconds, typical for dynamics of adsorbate at metallic surfaces. Further testing is made on the laser-induced intramolecular charge transfer in a quinone derivative as a model for a molecular switch. A modified scheme to treat ionizing states is proposed to reduce the computational burden associated with the density matrix propagation, and it is thoroughly tested and compared to the results obtained with the former model. The new approach scales favorably (similar to N(2)) with the number of configurations N used to represent the reduced density matrix in the rho-TDCI method, as compared to a N(3) scaling for the model in its original form.}, language = {en} } @article{ThielKlamrothStrauchetal.2011, author = {Thiel, Kerstin and Klamroth, Tillmann and Strauch, Peter and Taubert, Andreas}, title = {On the interaction of ascorbic acid and the tetrachlorocuprate ion [CuCl4](2-) in CuCl nanoplatelet formation from an ionic liquid precursor (ILP)}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {30}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp20648f}, pages = {13537 -- 13543}, year = {2011}, abstract = {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.}, language = {en} } @article{SchoenbornSaalfrankKlamroth2016, author = {Sch{\"o}nborn, Jan Boyke and Saalfrank, Peter and Klamroth, Tillmann}, title = {Controlling the high frequency response of H-2 by ultra-short tailored laser pulses: A time-dependent configuration interaction study}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {144}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4940316}, pages = {9}, year = {2016}, abstract = {We combine the stochastic pulse optimization (SPO) scheme with the time-dependent configuration interaction singles method in order to control the high frequency response of a simple molecular model system to a tailored femtosecond laser pulse. For this purpose, we use H-2 treated in the fixed nuclei approximation. The SPO scheme, as similar genetic algorithms, is especially suited to control highly non-linear processes, which we consider here in the context of high harmonic generation. Here, we will demonstrate that SPO can be used to realize a "non-harmonic" response of H2 to a laser pulse. Specifically, we will show how adding low intensity side frequencies to the dominant carrier frequency of the laser pulse and stochastically optimizing their contribution can create a high-frequency spectral signal of significant intensity, not harmonic to the carrier frequency. At the same time, it is possible to suppress the harmonic signals in the same spectral region, although the carrier frequency is kept dominant during the optimization. (C) 2016 AIP Publishing LLC.}, language = {en} } @article{SchwarzeMuellerDoscheetal.2007, author = {Schwarze, Thomas and Mueller, Holger and Dosche, Carsten and Klamroth, Tillmann and Mickler, Wulfhard and Kelling, Alexandra}, title = {Luminescence detection of open-shell transition-metal ions by photoinduced electron transfer controlled by internal charge transfer of a receptor}, doi = {10.1002/anie.200603992}, year = {2007}, language = {en} } @article{SchwarzeMicklerDoscheetal.2010, author = {Schwarze, Thomas and Mickler, Wulfhard and Dosche, Carsten and Flehr, Roman and Klamroth, Tillmann and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Saalfrank, Peter and Holdt, Hans-J{\"u}rgen}, title = {Systematic investigation of photoinduced electron transfer controlled by internal charge transfer and its consequences for selective PdCl2 coordination}, issn = {0947-6539}, doi = {10.1002/chem.200902281}, year = {2010}, abstract = {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.}, language = {en} } @article{SchwarzeMicklerDoscheetal.2010, author = {Schwarze, Thomas and Mickler, Wulfhard and Dosche, Carsten and Flehr, Roman and Klamroth, Tillmann and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Saalfrank, Peter and Holdt, Hans-J{\"u}rgen}, title = {Systematic investigation of photoinduced electron transfer controlled by internal charge transfer and its consequences for selective PdCl2 coordination}, issn = {0947-6539}, year = {2010}, abstract = {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.}, language = {en} } @article{SchwarzeKellingMuelleretal.2012, author = {Schwarze, Thomas and Kelling, Alexandra and M{\"u}ller, Holger and Trautmann, Michael and Klamroth, Tillmann and Baumann, Otto and Strauch, Peter and Holdt, Hans-J{\"u}rgen}, title = {N-2-Pyridinylmethyl-N '-arylmethyl-diaminomaleonitriles: New Highly Selective Chromogenic Chemodosimeters for Copper(II)}, series = {Chemistry - a European journal}, volume = {18}, journal = {Chemistry - a European journal}, number = {34}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201201731}, pages = {10506 -- 10510}, year = {2012}, language = {en} } @article{SchwarzeDoscheFlehretal.2010, author = {Schwarze, Thomas and Dosche, Carsten and Flehr, Roman and Klamroth, Tillmann and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Saalfrank, Peter and Cleve, Ernst and Buschmann, Hans-J{\"u}rgen and Holdt, Hans-J{\"u}rgen}, title = {Combination of a CT modulated PET and an intramolecular excimer formation to quantify PdCl2 by large fluorescence enhancement}, issn = {1359-7345}, doi = {10.1039/B919973j}, year = {2010}, abstract = {The [6.6](9,10)anthracenophane 1 (Scheme 1) is a selective fluoroionophore for the detection of PdCl2 with a large fluorescence enhancement factor (I/I-0 > 250).}, language = {en} } @article{SchwarzeDoscheFlehretal.2010, author = {Schwarze, Thomas and Dosche, Carsten and Flehr, Roman and Klamroth, Tillmann and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Saalfrank, Peter and Cleve, Ernst and Buschmann, Hans-J{\"u}rgen and Holdt, Hans-J{\"u}rgen}, title = {Combination of a CT modulated PET and an intramolecular excimer formation to quantify PdCl2 by large fluorescence enhancement}, issn = {1359-7345}, year = {2010}, language = {en} } @article{SaalfrankNestAndrianovetal.2006, author = {Saalfrank, Peter and Nest, Mathias and Andrianov, Igor V. and Klamroth, Tillmann and Kroner, Dominic and Beyvers, Stephanie}, title = {Quantum dynamics of laser-induced desorption from metal and semiconductor surfaces, and related phenomena}, volume = {18}, number = {30}, publisher = {IOP Publ.}, address = {Bristol}, issn = {1361-648X}, doi = {10.1088/0953-8984/18/30/S05}, pages = {S1425 -- S1459}, year = {2006}, abstract = {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)}, language = {en} } @article{SaalfrankKlamrothHuberetal.2005, author = {Saalfrank, Peter and Klamroth, Tillmann and Huber, C. and Krause, Pascal}, title = {Laser-driven electron dynamics at interfaces}, issn = {0021-2148}, year = {2005}, abstract = {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}, language = {en} } @incollection{SaalfrankBedurkeHeideetal.2020, author = {Saalfrank, Peter and Bedurke, Florian and Heide, Chiara and Klamroth, Tillmann and Klinkusch, Stefan and Krause, Pascal and Nest, Mathias and Tremblay, Jean Christophe}, title = {Molecular attochemistry: correlated electron dynamics driven by light}, series = {Advances in quantum chemistry}, volume = {81}, booktitle = {Advances in quantum chemistry}, editor = {Ruud, Kenneth and Br{\"a}ndas, Erkki J.}, publisher = {Elsevier}, address = {Amsterdam [u.a.]}, isbn = {978-0-12-819757-8}, issn = {0065-3276}, doi = {10.1016/bs.aiq.2020.03.001}, pages = {15 -- 50}, year = {2020}, abstract = {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).}, language = {en} } @article{ParamonovKlamrothLuetal.2018, author = {Paramonov, Guennaddi K. and Klamroth, Tillmann and Lu, H. Z. and Bandrauk, Andre D.}, title = {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}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {98}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {6}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.063431}, pages = {16}, year = {2018}, abstract = {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.}, language = {en} } @article{NestLudwigUlusoyetal.2013, author = {Nest, Mathias and Ludwig, M. and Ulusoy, I. and Klamroth, Tillmann and Saalfrank, Peter}, title = {Electron correlation dynamics in atoms and molecules}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {138}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {16}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4801867}, pages = {6}, year = {2013}, abstract = {In this paper, we present quantum dynamical calculations on electron correlation dynamics in atoms and molecules using explicitly time-dependent ab initio configuration interaction theory. The goals are (i) to show that in which cases it is possible to switch off the electronic correlation by ultrashort laser pulses, and (ii) to understand the temporal evolution and the time scale on which it reappears. We characterize the appearance of correlation through electron-electron scattering when starting from an uncorrelated state, and we identify pathways for the preparation of a Hartree-Fock state from the correlated, true ground state. Exemplary results for noble gases, alkaline earth elements, and selected molecules are provided. For Mg we show that the uncorrelated state can be prepared using a shaped ultrashort laser pulse.}, language = {en} } @article{NestKlamrothSaalfrank2005, author = {Nest, Mathias and Klamroth, Tillmann and Saalfrank, Peter}, title = {The multiconfiguration time-dependent Hartree-Fock method for quantum chemical calculations}, issn = {0021-9606}, year = {2005}, abstract = {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}, language = {en} } @article{NestKlamroth2005, author = {Nest, Mathias and Klamroth, Tillmann}, title = {Correlated many-electron dynamics : application to inelastic electron scattering at a metal film}, year = {2005}, abstract = {The multiconfiguration time-dependent Hartree-Fock and the time-dependent configuration interaction singles method are applied to the correlated many-electron dynamics of a one-dimensional jellium model system. We study the scattering of an initially free electron at a model film in the framework of both approaches. In particular, both methods are compared with regard to how they describe the underlying physical processes, namely inelastic electron scattering, inverse photoemission, and electron impact ionization}, language = {en} } @article{NacciFoelschZenichowskietal.2009, author = {Nacci, Christophe and Foelsch, Stefan and Zenichowski, Karl and Dokic, Jadranka and Klamroth, Tillmann and Saalfrank, Peter}, title = {Current versus temperature-induced switching in a single-molecule tunnel junction : 1,5 cyclooctadiene on Si(001)}, issn = {1530-6984}, doi = {10.1021/Nl901419g}, year = {2009}, abstract = {The biconformational switching of single cyclooctadiene molecules chemisorbed on a Si(001) surface was explored by quantum chemical and quantum dynamical calculations and low-temperature scanning tunneling microscopy experiments. The calculations rationalize the experimentally observed switching driven by inelastic electron tunneling (IET) at 5 K. At higher temperatures, they predict a controllable crossover behavior between IET-driven and thermally activated switching, which is fully confirmed by experiment.}, language = {en} } @article{MalicWeberRichteretal.2011, author = {Malic, E. and Weber, C. and Richter, M. and Atalla, V. and Klamroth, Tillmann and Saalfrank, Peter and Reich, Sebastian and Knorr, A.}, title = {Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.097401}, pages = {4}, year = {2011}, abstract = {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.}, language = {en} } @article{MaassUtechtStremlauetal.2017, author = {Maass, Friedrich and Utecht, Manuel Martin and Stremlau, Stephan and Gille, Marie and Schwarz, Jutta and Hecht, Stefan and Klamroth, Tillmann and Tegeder, Petra}, title = {Electronic structure changes during the on-surface synthesis of nitrogen-doped chevron-shaped graphene nanoribbons}, series = {Physical review : B, Condensed matter and materials physics}, volume = {96}, journal = {Physical review : B, Condensed matter and materials physics}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.96.045434}, pages = {7}, year = {2017}, abstract = {Utilizing suitable precursor molecules, a thermally activated and surface-assisted synthesis results in the formation of defect-free graphene nanoribbons (GNRs), which exhibit electronic properties that are not present in extended graphene. Most importantly, they have a band gap in the order of a few electron volts, depending on the nanoribbon width. In this study, we investigate the electronic structure changes during the formation of GNRs, nitrogen-doped (singly and doubly N-doped) as well as non-N-doped chevron-shaped CGNRs on Au(111). Thus we determine the optical gaps of the precursor molecules, the intermediate nonaromatic polymers, and finally the aromatic GNRs, using high-resolution electron energy loss spectroscopy and density functional theory calculations. As expected, we find no influence of N-doping on the size of the optical gaps. The gap of the precursor molecules is around 4.5 eV. Polymerization leads to a reduction of the gap to a value of 3.2 eV due to elongation and thus enhanced delocalization. The CGNRs exhibit a band gap of 2.8 eV, thus the gap is further reduced in the nanoribbons, since they exhibit an extended delocalized pi-electron system.}, language = {en} } @article{KroenerSchimkaKlamroth2014, author = {Kroener, Dominik and Schimka, Selina and Klamroth, Tillmann}, title = {Laser control for coupled torsions in chiroptical switches: a combined quantum and classical dynamics approach}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {118}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {2}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/jp410342a}, pages = {1322 -- 1331}, year = {2014}, abstract = {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.}, language = {en} } @article{KrauseKlamrothSaalfrank2005, author = {Krause, Pascal and Klamroth, Tillmann and Saalfrank, Peter}, title = {Time-dependent configuration-interaction calculations of laser-pulse-driven many-electron dynamics : Controlled dipole switching in lithium cyanide}, issn = {0021-9606}, year = {2005}, abstract = {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}, language = {en} } @article{KrausAschenbrennerKlamrothetal.2009, author = {Kraus, Florian and Aschenbrenner, J{\"u}rgen C. and Klamroth, Tillmann and Korber, Nikolaus}, title = {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}, issn = {0020-1669}, doi = {10.1021/Ic8014546}, year = {2009}, abstract = {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).}, language = {en} } @article{KlinkuschSaalfrankKlamroth2009, author = {Klinkusch, Stefan and Saalfrank, Peter and Klamroth, Tillmann}, title = {Laser-induced electron dynamics including photoionization : a heuristic model within time-dependent configuration interaction theory}, issn = {0021-9606}, doi = {10.1063/1.3218847}, year = {2009}, abstract = {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.}, language = {en} } @article{KlinkuschKlamrothSaalfrank2009, author = {Klinkusch, Stefan and Klamroth, Tillmann and Saalfrank, Peter}, title = {Long-range intermolecular charge transfer induced by laser pulses : an explicitly time-dependent configuration interaction approach}, issn = {1463-9076}, doi = {10.1039/B817873a}, year = {2009}, abstract = {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.}, language = {en} } @article{KlinkuschKlamroth2013, author = {Klinkusch, Stefan and Klamroth, Tillmann}, title = {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}, series = {Journal of theoretical and computational chemistry}, volume = {12}, journal = {Journal of theoretical and computational chemistry}, number = {3}, publisher = {World Scientific}, address = {Singapore}, issn = {0219-6336}, doi = {10.1142/S0219633613500053}, pages = {17}, year = {2013}, abstract = {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.}, language = {en} } @article{KlamrothNest2009, author = {Klamroth, Tillmann and Nest, Mathias}, title = {Ultrafast electronic excitations of small sodium clusters and the onset of electron thermalization}, issn = {1463-9076}, doi = {10.1039/B813619j}, year = {2009}, abstract = {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.}, language = {en} } @article{KlamrothKronerSaalfrank2005, author = {Klamroth, Tillmann and Kroner, Dominic and Saalfrank, Peter}, title = {Laser-driven coupled electron-nuclear dynamics : Quantum mechanical simulation of molecular photodesorption from metal films}, issn = {1098-0121}, year = {2005}, abstract = {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}, language = {en} } @article{Klamroth2006, author = {Klamroth, Tillmann}, title = {Optimal control of ultrafast laser driven many-electron dynamics in a polyatomic molecule: N-methyl-6-quinolone}, issn = {0021-9606}, doi = {10.1063/1.2185633}, year = {2006}, abstract = {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.}, language = {en} } @phdthesis{Klamroth2006, author = {Klamroth, Tillmann}, title = {Quantum mechanical simulations for correlated many-electron dynamics and electron induced processes at surfaces}, address = {Potsdam}, pages = {206 S. : graph. Darst.}, year = {2006}, language = {en} } @article{Klamroth2003, author = {Klamroth, Tillmann}, title = {Laser-driven electron transfer through metal-insulator-metal contacts : time-dependent configuration interaction singles calculations for a jellium model}, issn = {1098-0121}, year = {2003}, abstract = {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}, language = {en} } @article{HuberKlamroth2011, author = {Huber, Christian and Klamroth, Tillmann}, title = {Explicitly time-dependent coupled cluster singles doubles calculations of laser-driven many-electron dynamics}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {134}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {5}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.3530807}, pages = {8}, year = {2011}, abstract = {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.}, language = {en} } @article{HuberKlamroth2005, author = {Huber, C. and Klamroth, Tillmann}, title = {Simulation of two-photon-photoelectron spectra at a jellium-vacuum interface}, year = {2005}, abstract = {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}, language = {en} } @article{GaebelBeinMathaueretal.2021, author = {Gaebel, Tina and Bein, Daniel and Mathauer, Daniel and Utecht, Manuel and Palmer, Richard E. and Klamroth, Tillmann}, title = {Nonlocal STM manipulation of chlorobenzene on Si(111)-7 x 7}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {125}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {22}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.1c02612}, pages = {12175 -- 12184}, year = {2021}, abstract = {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.}, language = {en} } @article{FuechselTremblayKlamrothetal.2012, author = {F{\"u}chsel, Gernot and Tremblay, Jean Christophe and Klamroth, Tillmann and Saalfrank, Peter and Frischkorn, C.}, title = {Concept of a single temperature for highly nonequilibrium laser-induced hydrogen desorption from a ruthenium surface}, series = {Physical review letters}, volume = {109}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.109.098303}, pages = {5}, year = {2012}, abstract = {Laser-induced condensed phase reactions are often interpreted as nonequilibrium phenomena that go beyond conventional thermodynamics. Here, we show by Langevin dynamics and for the example of femtosecond-laser desorption of hydrogen from a ruthenium surface that light adsorbates thermalize rapidly due to ultrafast energy redistribution after laser excitation. Despite the complex reaction mechanism involving hot electrons in the surface region, all desorption product properties are characterized by equilibrium distributions associated with a single, unique temperature. This represents an example of ultrahot chemistry on the subpicosecond time scale.}, language = {en} } @article{FuechselTremblayKlamrothetal.2012, author = {F{\"u}chsel, Gernot and Tremblay, Jean Christophe and Klamroth, Tillmann and Saalfrank, Peter}, title = {Selective excitation of molecule-surface vibrations in H2 and D2 dissociatively adsorbed on Ru(0001)}, series = {Israel journal of chemistry}, volume = {52}, journal = {Israel journal of chemistry}, number = {5}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0021-2148}, doi = {10.1002/ijch.201100097}, pages = {438 -- 451}, year = {2012}, abstract = {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.}, language = {en} }