@article{KopfSaalfrank2004, author = {Kopf, A. and Saalfrank, Peter}, title = {Electron transport through molecules treated by LCAO-MO Green's functions with absorbing boundaries}, issn = {0009-2614}, year = {2004}, abstract = {In this Letter, we present a method for calculating transport properties of molecular conductors using a time- independent scattering approach based on Green's functions with absorbing boundaries. The method, which has been used before for chemical reaction dynamics in a grid basis [Seideman, Miller, J. Chem. Phys. 96 (1992) 4412], is formulated here in an LCAO-MO form within simple Huckel theory and extended Huckel theory (EHT), respectively. Test calculations are for a quasi-one-dimensional atom chain. As a more realistic application, the organic molecules benzene- 1,4-dithiolate and biphenyl-4,4'-dithiolate between gold electrodes are studied. (C) 2004 Elsevier B.V. All rights reserved}, language = {en} } @article{NeissSaalfrank2004, author = {Neiss, C. and Saalfrank, Peter}, title = {Molecular dynamics simulation of the LOV2 domain from Adiantum capillus-veneris}, issn = {0095-2338}, year = {2004}, abstract = {The mechanism for signal transduction from the LOV-domains toward the kinase region of phototropin is still not well understood. We have performed molecular dynamics (MD) simulations and CONCOORD calculations on the LOV2 domain of Adiantum capillus-veneris, with the goal to detect possible differences between the two forms of the LOV domain which may not show up in the static crystal structures. Since no such clear differences are found in the MD simulations also, we suggest that the real, biologically active conformation of the LOV domain within the whole phototropin is different from the crystal structure of the isolated LOV domains. The MD simulations do offer, however, insight into details of the dynamics of the dark and illuminated LOV domains, which are discussed in the light of recent experiments}, language = {en} } @article{NestSaalfrank2004, author = {Nest, Mathias and Saalfrank, Peter}, title = {Enhancement of femtosecond-laser-induced molecular desorption by thin metal films}, year = {2004}, abstract = {We investigate femtosecond-laser induced desorption [desorption induced by multiple electronic transitions (DIMET)] of NO molecules from thin Pt(111) films. On the basis of a two-state, open-system density matrix treatment in combination with a two-temperature model, we argue that decreasing the film thickness enhances desorption cross sections by orders of magnitude in comparison to bulk materials. Both the spatial confinement and the laser fluence appear therefore as efficient, nonlinear enhancement factors for nonadiabatic photoreactions of metal surfaces and, possibly, of nanostructered materials in general}, language = {en} } @article{Saalfrank2004, author = {Saalfrank, Peter}, title = {Theory of photon- and STM-induced bond cleavage at surfaces}, issn = {1359-0286}, year = {2004}, abstract = {In this contribution, recent advances in the theory of laser and, to a lesser extent, of scanning tunneling microscope (STM) induced cleavage of bonds between an adsorbate and a solid surface, will be reviewed. Special emphasis will be given to the quantum dynamics of electronically non-adiabatic reactions. (c) 2005 Elsevier Ltd. All rights reserved}, 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{AndrianovKlamrothSaalfranketal.2005, author = {Andrianov, Igor V. and Klamroth, Tillmann and Saalfrank, Peter and Bovensiepen, U. and Gahl, Cornelius and Wolf, M. M.}, title = {Quantum theoretical study of electron solvation dynamics in ice layers on a Cu(111) surface}, issn = {0021-9606}, year = {2005}, abstract = {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}, 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} } @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{MaterzaniniTantardiniLindanetal.2005, author = {Materzanini, G. and Tantardini, G. F. and Lindan, P. J. D. and Saalfrank, Peter}, title = {Water adsorption at metal surfaces : a first-principles study of the p(root 3x root 3)R30 degrees H2O bilayer on Ru(0001)}, issn = {1098-0121}, year = {2005}, abstract = {In the light of recent intensity-voltage low energy electron diffraction (LEED-IV) experiments [Surf. Sci. 316, 92 (1994); Surf. Rev. Lett. 10, 487 (2003)], the electronic and geometric structure of a water bilayer adsorbed at the Ru(0001) surface are investigated through first-principles total energy calculations, using periodic slab geometries and gradient-corrected density functional theory (DFT). We consider five possible bilayer structures, all roughly consistent with the LEED-IV analysis (three intact structures and two half-dissociated), and a water single layer at Ru(0001). Adsorption energies and substrate-adsorbate geometry parameters are given and discussed in the light of the experiments. We also give a comparative analysis of the electron density redistribution (Delta rho) and of the dipole moment change (Delta mu) induced by water adsorption on the Ru(0001) surface. In agreement with Feibelman [Science 295, 99 (2002)], the half-dissociated structures are found to be more stable than the intact ones, and their adsorption geometries in better agreement with the LEED-IV data. However, the Delta rho analysis shows that a half-dissociated structure induces a Delta mu>0, which would be incompatible with the experimentally measured decrease of the work function following bilayer adsorption; the latter would be consistent, instead, with the Delta mu < 0 induced by the intact structures. It is the aim of this paper to compare various possible adsorption structures, most of them already considered previously, with one and the same method. For this purpose, thick slabs and restrictive computational parameters are chosen to generally address the accuracy and the limits of DFT in reproducing adsorption energies and bond lengths of water-metal interacting systems}, 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{MartinazzoNestSaalfranketal.2006, author = {Martinazzo, Rocco and Nest, Mathias and Saalfrank, Peter and Tantardini, Gian Franco}, title = {A local coherent-state approximation to system-bath quantum dynamics}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {125}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {19}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.2362821}, pages = {16}, year = {2006}, abstract = {A novel quantum method to deal with typical system-bath dynamical problems is introduced. Subsystem discrete variable representation and bath coherent-state sets are used to write down a multiconfigurational expansion of the wave function of the whole system. With the help of the Dirac-Frenkel variational principle, simple equations of motion-a kind of Schrodinger-Langevin equation for the subsystem coupled to (pseudo) classical equations for the bath-are derived. True dissipative dynamics at all times is obtained by coupling the bath to a secondary, classical Ohmic bath, which is modeled by adding a friction coefficient in the derived pseudoclassical bath equations. The resulting equations are then solved for a number of model problems, ranging from tunneling to vibrational relaxation dynamics. Comparison of the results with those of exact, multiconfiguration time-dependent Hartree calculations in systems with up to 80 bath oscillators shows that the proposed method can be very accurate and might be of help in studying realistic problems with very large baths. To this end, its linear scaling behavior with respect to the number of bath degrees of freedom is shown in practice with model calculations using tens of thousands of bath oscillators.}, language = {en} } @article{AndrianovSaalfrank2006, author = {Andrianov, Ivan and Saalfrank, Peter}, title = {Free vibrational relaxation of H adsorbed on a Si(100) surface investigated with the multi-configurational time-dependent Hartree method}, series = {Chemical physics letters}, volume = {433}, journal = {Chemical physics letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2614}, doi = {10.1016/j.cplett.2006.11.067}, pages = {91 -- 96}, year = {2006}, abstract = {The results of a quantum-mechanical study of vibrational relaxation of hydrogen adsorbed on a Si(100) surface with the multi-configurational time-dependent Hartree (MCTDH) method are presented. A two-dimensional subsystem is coupled non-linearly to a bath of harmonic oscillators (phonons of the Si bulk), and the relaxation of subsystem vibrations proceeds primarily via a two-phonon process. Characteristic times of the system evolution agree well with our previous perturbation theory study. The vibrational population decay is non-exponential, exhibiting pronounced recurrences due to finite bath size. The dependence of the lifetimes of the vibrational levels on the bath size and on the coupling details is investigated.}, language = {en} } @article{FuechselKlamrothDokicetal.2006, author = {F{\"u}chsel, Gernot and Klamroth, Tillmann and Dokic, Jadranka and Saalfrank, Peter}, title = {On the electronic structure of neutral and ionic azobenzenes and their possible role as surface mounted molecular switches}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {110}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {33}, publisher = {Soc.}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp060969v}, pages = {16337 -- 16345}, year = {2006}, abstract = {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.}, language = {en} } @article{Saalfrank2006, author = {Saalfrank, Peter}, title = {Quantum dynamical approach to ultrafast molecular desorption from surfaces}, series = {Chemical reviews}, volume = {106}, journal = {Chemical reviews}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {0009-2665}, doi = {10.1021/cr0501691}, pages = {4116 -- 4159}, year = {2006}, language = {en} } @article{AndrianovSaalfrank2006, author = {Andrianov, Ivan and Saalfrank, Peter}, title = {Theoretical study of vibration-phonon coupling of H adsorbed on a Si(100) surface}, issn = {0021-9606}, doi = {10.1063/1.2161191}, year = {2006}, abstract = {In this paper a perturbation-theory study of vibrational lifetimes for the bending and stretching modes of hydrogen adsorbed on a Si(100) surface is presented. The hydrogen-silicon interaction is treated with a semiempirical bond-order potential. Calculations are performed for H-Si clusters of different sizes. The finite lifetime is due to vibration-phonon coupling, which is assumed to be linear or bilinear in the phonon and nonlinear in the H-Si stretching and bending modes. Lifetimes and vibrational transition rates are evaluated with one- and two-phonon processes taken into account. Temperature effects are also discussed. In agreement with the experiment and previous theoretical treatment it is found that the H-Si (upsilon(s)=1) stretching vibration decays on a nanosecond timescale, whereas for the H-Si (upsilon(b)=1) bending mode a picosecond decay is predicted. For higher-excited vibrations, simple scaling laws are found if the excitation energies are not too large. The relaxation mechanisms for the excited H-Si stretching and the H-Si bending modes are analyzed in detail.}, language = {en} } @article{BeyversOhtsukiSaalfrank2006, author = {Beyvers, Stephanie and Ohtsuki, Y and Saalfrank, Peter}, title = {Optimal control in a dissipative system : vibrational excitation of CO/Cu(100) by IR pulses}, issn = {0021-9606}, doi = {10.1063/1.2206593}, year = {2006}, abstract = {The question as to whether state-selective population of molecular vibrational levels by shaped infrared laser pulses is possible in a condensed phase environment is of central importance for such diverse fields as time-resolved spectroscopy, quantum computing, or "vibrationally mediated chemistry." This question is addressed here for a model system, representing carbon monoxide adsorbed on a Cu(100) surface. Three of the six vibrational modes are considered explicitly, namely, the CO stretch vibration, the CO-surface vibration, and a frustrated translation. Optimized infrared pulses for state-selective excitation of "bright" and "dark" vibrational levels are designed by optimal control theory in the framework of a Markovian open-system density matrix approach, with energy flow to substrate electrons and phonons, phase relaxation, and finite temperature accounted for. The pulses are analyzed by their Husimi "quasiprobability" distribution in time-energy space.}, 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{ParamonovSaalfrank2009, author = {Paramonov, Guennaddi K. and Saalfrank, Peter}, title = {Time-evolution operator method for non-Markovian density matrix propagation in time and space representation : application to laser association of OH in an environment}, issn = {1050-2947}, doi = {10.1103/Physreva.79.013415}, year = {2009}, abstract = {An efficient method for the numerical solution of a non-Markovian, open-system density matrix equation of motion in coordinate representation is developed. We apply the scheme to model simulations of the laser-assisted O+H -> OH association reaction in an environment. The suggested approach is based on the application of the time-evolution operator to the "closed-system" part of the overall Hamiltonian and transformation of the open-system equation of motion to the Heisenberg picture suitable for numerical propagation. A dual role of the system-environment coupling with respect to the infrared (ir) laser-driven association of OH is demonstrated: the association probability is increased due to the coupling at relatively weak laser fields, but decreased at strong laser fields. Moreover, at a certain strength of the ir laser field, the association probability does not depend on the strength of the system-bath coupling at all.}, language = {en} } @article{TremblaySaalfrank2009, author = {Tremblay, Jean Christophe and Saalfrank, Peter}, title = {Selective subsurface absorption of hydrogen in palladium using laser distillation}, issn = {0021-9606}, doi = {10.1063/1.3212695}, year = {2009}, abstract = {A theoretical model for the selective subsurface absorption of atomic hydrogen in a Pd(111) surface by infrared (IR) laser pulses is presented. The dynamics of the adsorbate is studied within the reduced density matrix approach. Energy and phase relaxation of the hydrogen atom are treated using the semigroup formalism. The vibrational excitation leading to subsurface absorption is performed using rationally designed pulses as well as IR laser pulses optimized on- the-fly. It is shown that dissipation can be used as a tool to transfer population to an otherwise inaccessible state via a mechanism known as "laser distillation." We demonstrate that when the reaction path is generalized from a reduced one-dimensional to full three-dimensional treatment of the system, the laser control strategy can prove very different.}, language = {en} } @article{GoetzeSaalfrank2009, author = {G{\"o}tze, Jan and Saalfrank, Peter}, title = {Serine in BLUF domains displays spectral importance in computational models}, issn = {1011-1344}, doi = {10.1016/j.jphotobiol.2008.10.003}, year = {2009}, abstract = {The BLUF (blue-light sensing using flavine) domain of the AppA photoreceptor protein from Rhodobacter sphaeroides was modelled by using quantum chemical chromophore plus amino acid models at the (TD-)B3LYP/6-31G* level of theory. The models were based on NMR structures, and further refined by CHARM force field molecular dynamics simulations. The goal is to explain the total redshift by about 10 nm in the UV/Vis spectra of BLUF domains after illumination, and to relate it to structural changes. For this purpose UV/Vis spectra of the available NMR structures were calculated and related to geometrical features. In particular, the hydrogen network embedding the central chromophore is discussed. Specifically, the position of a conserved glutamine, Q63, is found to be important in agreement with findings from previous works. Additionally, however, we find a systematic dependence also on the geometry of a conserved serine, S41. Based on a series of calculations with known structures and with artificial structural models, we argue that indeed the light-induced switching of both Q63 and S41 is necessary to explain the full similar to 10 nm redshift in the light (signalling) state of serine containing BLUF domains. Following or accompanying the double switching, two structurally highly important residues W104 and M106 exchange places, but do not affect the overall UV/ Vis properties of the chromophore.}, language = {en} }