@incollection{BonačićKouteckyHartmannPittneretal.2000, author = {Bonačić-Kouteck{\´y}, Vlasta and Hartmann, Michael and Pittner, Jiř{\i}́ and Dam, Huub van}, title = {Theoretical exploration of single and multi state femtosecond nuclear dynamics of small metallic clusters using the DF method}, series = {Recent Advances in Density Functional Methods: Part 3}, booktitle = {Recent Advances in Density Functional Methods: Part 3}, editor = {Barone, Vincenzo and Bencini, Alessandro and Fantucci, Piercarlo}, publisher = {World Scientific}, address = {Singapore}, publisher = {SRH Berlin University of Applied Sciences}, pages = {Keine Angabe - No details -- Keine Angabe - No details}, year = {2000}, abstract = {Keine Angabe - No details}, language = {en} } @article{HartmannPittnerDametal.1999, author = {Hartmann, Michael and Pittner, Jiř{\i}́ and Dam, Huub van and Bonačić-Kouteck{\´y}, Vlasta}, title = {Theoretical study of femtosecond pump-probe signals of nonstoichiometric alkali halide clusters}, series = {The European Physical Journal D}, volume = {9}, journal = {The European Physical Journal D}, number = {1}, url = {http://nbn-resolving.de/urn:nbn:de:0298-opus4-5640}, pages = {393 -- 397}, year = {1999}, abstract = {We present the outline of the ab-initio molecular dynamics method for adiabatic excited states which is suitable to treat the involved excited electronic states simultaneously with the motion of the nuclei. The method allows the simulation of time-resolved pump-probe signals and the analysis of the signals in terms of the underlying nuclear dynamics. Moreover, the timescales of the structural relaxation in excited electronic states vs. intramolecular vibrational relaxation processes can be estimated and the influence of the initial temperature of the cluster can be determined. The method is applied to the analysis of the timescales as well as of the dynamics of localized/delocalized electronic excitations in the Na2F molecule which represents a test example for nonstoichiometric alkali-halides with one excess electron. The aim is to develop a method for the investigation of time-dependent laser induced processes in clusters which is capable to extract the leading physical effects responsible for the controlled excitation dynamics and for the evolution of the non-equilibrium states.}, language = {en} } @article{HartmannPittnerDametal.2000, author = {Hartmann, Michael and Pittner, Jiř{\i}́ and Dam, Huub van and Veyret, Vincent and Bonacic-Kouteck{\´y}, Vlasta}, title = {Theoretical exploration of stationary and of ultrafast spectroscopy of small clusters}, series = {Applied Physics B}, volume = {71}, journal = {Applied Physics B}, number = {3}, url = {http://nbn-resolving.de/urn:nbn:de:0298-opus4-5693}, pages = {343 -- 349}, year = {2000}, abstract = {Stationary spectra offer information on the interplay between the structures and the nature of electronic excitations reflecting bonding properties, as shown by comparing Sin with Agn (n=4-6) clusters. In order to study the dynamical properties, simulations and analysis of femtosecond (fs) time-resolved pump-probe or pump-dump signals have been carried out, which allows us to determine the timescales and the nature of configurational changes versus internal vibrational relaxation (IVR) in electronic ground or excited states. For this purpose we have developed a multi-state ab initio molecular dynamics (involving ground as well as adiabatic or non-adiabatic excited electronic states) on the timescale of the nuclear motion, using the time evolution of a thermal ensemble in the Wigner representation. The combination of ab initio quantum-chemical methods used for the molecular dynamics 'on the fly' and the Wigner-distribution approach for the description of the motion of the nuclei also allowed the accurate determination of pump-probe and pump-dump signals under temperature-dependent initial conditions. We use this novel combination of methods to investigate the dynamics in excited states of non-stoichiometric NanFn-1 clusters with a single excess electron. The timescales of the structural relaxation in excited states versus intramolecular vibrational relaxation processes have been determined, as illustrated for the example of Na4F3. This is the first study of the system with 15 degrees of freedom for which the dynamics in the excited states has been carried out without the precalculation of the energy surfaces.}, language = {en} } @article{BonačićKouteckyHartmannPittneretal.2001, author = {Bonačić-Kouteck{\´y}, Vlasta and Hartmann, Michael and Pittner, Jiř{\i}́ and Dam, Huub van}, title = {Theoretical exploration of ultrafast spectroscopy of small clusters}, series = {International Journal of Quantum Chemistry}, volume = {84}, journal = {International Journal of Quantum Chemistry}, number = {6}, url = {http://nbn-resolving.de/urn:nbn:de:0298-opus4-5712}, pages = {714 -- 739}, year = {2001}, abstract = {The central issue in femtosecond (fs) time resolved spectroscopy of clusters is the investigation of geometric relaxation and internal vibrational redistribution (IVR) after optical excitation in a nonequilibrium configuration of nuclei by laser photoelectron excitation, and corresponding time delayed probing by multiphoton-ionization. For this purpose, we have developed multistate ab initio molecular dynamics involving adiabatic ground and excited electronic states, as well as nonadiabatic coupling between them, using the time evolution of initial thermal ensemble in Wigner representation. The combination of ab initio quantum chemical methods, used for the adiabatic and nonadiabatic molecular dynamics "on the fly," and the Wigner distribution approach for the description of the motion of the nuclei allowed us the accurate determination of pump-probe and pump-dump signals also under temperature dependent initial conditions. The connection between simulated pump-probe signals and the underlying dynamics of nuclei involving adiabatic electronic ground states has been first established for the example of the Agequation image/Ag3/Agequation image systems, and compared with experimental negative-to-neutral-to-positive NeNePo pump-probe signals. Our simulations reproduced the experimental NeNePo results and determined, in addition to the timescales of geometric relaxation, the conditions under which the resonant or dissipative IVR, as well as vibrational coherence, should be found in the experimental pump-probe signals. This can be realized in the zero electron kinetic energy NeNePo-ZEKE experiments, which are in progress. The above combination of methods has been recently extended to the analysis of the timescales as well as of the dynamics in excited electronic states of the nonstoichiometric NanFn-1 (n=2-4) clusters with the single excess valence electron. Our approach allows the simulation of femtosecond NeExPo-pump-probe and NeExNe-pump-dump signals, based on an analytic formulation which utilizes temperature dependent ground state initial conditions of neutral system (Ne); an ensemble of trajectories carried out either on the adiabatic electronic excited state (Ex), or on both the excited and the ground states through nonadiabatic coupling in connection with the fewest switching hopping algorithm for the investigation of the dynamics of the system; and either the cationic (Po) or the neutral ground state (Ne) for the probing step. The choice of the systems has been made in order to determine the timescales of processes involving (1) fast geometric relaxation leaving the bonding frame intact versus IVR, as during the adiabatic dynamics in the first excited state of Na4F3, being the smallest prototype of F-colored centers in the bulk; and (2) the photo-isomerization process through the conical intersection during nonadiabatic dynamics due to the long amplitude motion, as in the Na3F2 cluster after breaking of one metallic and one ionic bond, representing the first example of a five atomic cluster in the gas phase exhibiting conical intersection between the ground and the first excited state. In both cases, full complexity of the problem has been considered taking into account all degrees of freedom. The investigated systems represent important test cases for providing the conceptual framework of ultrafast dynamics in finite systems.}, language = {en} }