TY - JOUR A1 - Schäfer-Bung, Boris A1 - Nest, Mathias T1 - Correlated dynamics of electrons with reduced 2-electron density matrices N2 - We present an approach to the correlated dynamics of many-electron systems. We show, that the two-electron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented. Y1 - 2008 UR - http://dx.doi.org/10.1103/PhysRevA.78.012512 ER - TY - GEN A1 - Schäfer-Bung, Boris A1 - Nest, Mathias T1 - Correlated dynamics of electrons with reduced two-electron density matrices N2 - We present an approach to the correlated dynamics of many-electron systems. We show, that the twoelectron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 100 Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41774 SN - 1866-8372 ER - TY - JOUR A1 - Saalfrank, Peter A1 - Nest, Mathias A1 - Andrianov, Igor V. A1 - Klamroth, Tillmann A1 - Kroner, Dominic A1 - Beyvers, Stephanie T1 - Quantum dynamics of laser-induced desorption from metal and semiconductor surfaces, and related phenomena N2 - Recent progress towards a quantum theory of laser-induced desorption and related phenomena is reviewed, for specific examples. These comprise the photodesorption of NO from Pt(111), the scanning tunnelling microscope and laser- induced desorption and switching of H at Si(100), and the electron stimulated desorption and dissociation of CO at Ru(0001). The theoretical methods used for nuclear dynamics range from open-system density matrix theory over nonadiabatically coupled multi-state models to electron-nuclear wavepackets. Also, aspects of time-dependent spectroscopy to probe ultrafast nonadiabatic processes at surfaces will be considered for the example of two-photon photoemission of solvated electrons in ice layers on Cu(111) Y1 - 2006 UR - http://iopscience.iop.org/0953-8984/18/30/S05/pdf/0953-8984_18_30_S05.pdf U6 - https://doi.org/10.1088/0953-8984/18/30/S05 SN - 1361-648X SN - 0953-8984 VL - 18 IS - 30 SP - S1425 EP - S1459 PB - IOP Publ. CY - Bristol ER - TY - CHAP A1 - Saalfrank, Peter A1 - Bedurke, Florian A1 - Heide, Chiara A1 - Klamroth, Tillmann A1 - Klinkusch, Stefan A1 - Krause, Pascal A1 - Nest, Mathias A1 - Tremblay, Jean Christophe ED - Ruud, Kenneth ED - Brändas, Erkki J. T1 - Molecular attochemistry: correlated electron dynamics driven by light T2 - Advances in quantum chemistry N2 - Modern laser technology and ultrafast spectroscopies have pushed the timescales for detecting and manipulating dynamical processes in molecules from the picosecond over femtosecond domains, to the attosecond regime (1 as = 10(-18) s). This way, real-time dynamics of electrons after their photoexcitation can be probed and manipulated. In particular, experiments are moving more and more from atomic and solid state systems to molecules, opening the fields of "molecular electron dynamics" and "attosecond chemistry." Also on the theory side, powerful quantum dynamical tools have been developed to rationalize experiments on ultrafast electron dynamics in molecular species.
In this contribution, we concentrate on theoretical aspects of ultrafast electron dynamics in molecules, mostly driven by lasers. The dynamics will be described with the help of wavefunction-based ab initio methods such as time-dependent configuration interaction (TD-CI) or the multiconfigurational time-dependent Hartree-Fock (MCTDHF) methods. Besides a survey of the methods and their extensions toward, e.g., treatment of ionization, laser pulse optimization, and open quantum systems, two specific examples of applications will be considered: The creation and/or dynamical fate of electronic wavepackets, and the nonlinear optical response to laser pulse excitation in molecules by high harmonic generation (HHG). KW - dipole approximation KW - electron dynamics KW - electronic wavepackets KW - high harmonic generation KW - ionization KW - optimal control theory KW - time-dependent Schrödinger equation Y1 - 2020 SN - 978-0-12-819757-8 U6 - https://doi.org/10.1016/bs.aiq.2020.03.001 SN - 0065-3276 VL - 81 SP - 15 EP - 50 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Nest, Mathias A1 - Saalfrank, Peter T1 - Enhancement of femtosecond-laser-induced molecular desorption by thin metal films N2 - 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 Y1 - 2004 ER - TY - JOUR A1 - Nest, Mathias A1 - Ludwig, M. A1 - Ulusoy, I. A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Electron correlation dynamics in atoms and molecules JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1063/1.4801867 SN - 0021-9606 SN - 1089-7690 VL - 138 IS - 16 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Nest, Mathias A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - The multiconfiguration time-dependent Hartree-Fock method for quantum chemical calculations N2 - We apply the multiconfiguration time-dependent Hartree-Fock method to electronic structure calculations and show that quantum chemical information can be obtained with this explicitly time-dependent approach. Different equations of motion are discussed, as well as the numerical cost. The two-electron integrals are calculated using a natural potential expansion, of which we describe the convergence behavior in detail Y1 - 2005 SN - 0021-9606 ER - TY - JOUR A1 - Nest, Mathias A1 - Klamroth, Tillmann T1 - Correlated many-electron dynamics : application to inelastic electron scattering at a metal film N2 - 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 Y1 - 2005 ER - TY - THES A1 - Nest, Mathias T1 - Quantum dynamics for large systems : system-bath type situations and correlated dynamics of many electrons Y1 - 2007 CY - Potsdam ER - TY - THES A1 - Nest, Mathias T1 - Quantum dynamics for large systems: System-bath type situations and correlated dynamics of many electrons Y1 - 2007 CY - Potsdam ER -