@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} } @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{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{EhlertKlamroth2017, author = {Ehlert, Christopher and Klamroth, Tillmann}, title = {The quest for best suited references for configuration interaction singles calculations of core excited states}, series = {Journal of computational chemistry : organic, inorganic, physical, biological}, volume = {38}, journal = {Journal of computational chemistry : organic, inorganic, physical, biological}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0192-8651}, doi = {10.1002/jcc.24531}, pages = {116 -- 126}, year = {2017}, abstract = {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.}, 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{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{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{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{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} }