@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{AndrianovBonačićKouteckyHartmannetal.2000, author = {Andrianov, Igor and Bonačić-Kouteck{\´y}, Vlasta and Hartmann, Michael and Manz, J{\"o}rn and Pittner, Jiř{\i}́ and Sundermann, K.}, title = {Ab initio three-dimensional quantum dynamics of Ag3 clusters in the NeNePo process}, series = {Chemical Physics Letters}, volume = {318}, journal = {Chemical Physics Letters}, number = {1-3}, url = {http://nbn-resolving.de/urn:nbn:de:0298-opus4-5637}, pages = {256 -- 262}, year = {2000}, abstract = {The first three-dimensional quantum-dynamical ab initio simulation of the large amplitude vibrational dynamics of an Ag3 cluster initiated from its linear transition state is presented. This can be monitored by femtosecond pump-probe negative-ion to neutral-to-positive-ion spectroscopy with zero electron kinetic energy (NeNePo-ZEKE). The time evolution of the representative wavepacket confirms the dynamical effects which have been discovered previously by Wigner-type semiclassical simulations: the initial coherent bending and stretching from linear to near equilateral triangular configuration, followed by intracluster collision and intracluster vibrational relaxation with a weak fractional revival. In addition, the quantum wavepacket shows interferences and spreading.}, 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{HartmannHeidenreichPittneretal.1998, author = {Hartmann, Michael and Heidenreich, Andreas and Pittner, Jiř{\i}́ and Bonačić-Kouteck{\´y}, Vlasta and Jortner, Joshua}, title = {Ultrafast Dynamics of Small Clusters on the Time Scale of Nuclear Motion}, series = {The Journal of Physical Chemistry A}, volume = {102}, journal = {The Journal of Physical Chemistry A}, number = {23}, pages = {4069 -- 4074}, year = {1998}, abstract = {We present a theoretical study of the multistate dynamics of the Ag3-/Ag3/Ag3+ system on the time scale of nuclear motion, as explored by femtosecond pump-probe negative ion-to neutral-to positive ion (NENEPO) spectroscopy. The dynamics of the Ag3 cluster initiated from its linear transition state involves configurational relaxation, intracluster collision, and onset of IVR, resonant and dissipative IVR and vibrational equilibration, whose time scales were determined. Our analysis reveals that theory is essential for the elucidation of the rich dynamic information regarding geometrical change, completion of IVR, and vibrational coherence effects in the NENEPO femtosecond signals.}, 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} } @article{HartmannPittnerBonačićKouteckyetal.1998, author = {Hartmann, Michael and Pittner, Jiř{\i}́ and Bonačić-Kouteck{\´y}, Vlasta and Heidenreich, Andreas and Jortner, Joshua}, title = {Theoretical exploration of femtosecond multi-state nuclear dynamics of small clusters}, series = {The Journal of Chemical Physics}, volume = {108}, journal = {The Journal of Chemical Physics}, number = {8}, pages = {3096 -- 3113}, year = {1998}, abstract = {We investigate ultrafast multi-state nuclear dynamics in a triatomic cluster. In particular, we explore how the intracluster nuclear dynamics of the Ag-3/Ag3/Ag+3 system is reflected in the femtosecond pump-probe negative ion-to neutral-to positive ion (NENEPO) signals. The nuclear dynamics is based on classical trajectories on the ground electronic adiabatic state potential hypersurfaces obtained from accurate ab initio quantum chemistry calculations. The nuclear dynamics of Ag3 initiated from the linear transition state involves distinct sequential processes of configurational relaxation to the triangular configuration, intracluster collisions, and the onset of IVR, resonant, and dissipative IVR, and vibrational equilibration. We determined the timescales for these processes and discussed their dependence on the initial cluster temperature. The Wigner representation of the density matrix was utilized to simulate the NENEPO-zero kinetic energy (NENEPO-ZEKE) signal and the total (integrated over the photoelectron energy) NENEPO signal. We show how geometrical change, completion of IVR and vibrational coherenceeffects can be identified in the NENEPO signals. A comparison of the calculated NENEPO signals with the available experimental data is presented.}, language = {en} } @article{BonačićKouteckyPittnerPouAmerigoetal.1997, author = {Bonačić-Kouteck{\´y}, Vlasta and Pittner, Jiř{\i}́ and Pou-Am{\´e}rigo, Rosendo and Hartmann, Michael}, title = {Ab-initio study of structural and optical properties of nonstoichiometric alkalimetal- oxides}, series = {Zeitschrift f{\"u}r Physik D}, volume = {40}, journal = {Zeitschrift f{\"u}r Physik D}, number = {1}, url = {http://nbn-resolving.de/urn:nbn:de:0298-opus4-5748}, pages = {445 -- 447}, year = {1997}, abstract = {Structural and optical properties of nonstoichiometric LinO and NanO (n = 3, 4) clusters containing one and two excess electrons are studied using ab-initio methods accounting for electron correlation. We show that calculated absorption patterns are excellent fingerprints of structural and bonding properties. The optical response of Li4O and Na4O clusters with the most stable tetrahedral type structures is characterized by a common feature, that is the appearance of a dominant intense transition in infrared regime although excess of electrons are not localized, as it is the case for small alkali-halide clusters, with cuboid corner vacancy (surface F-center in finite systems).}, language = {en} } @article{MitrićHartmannStancaetal.2001, author = {Mitrić, Roland and Hartmann, Michael and Stanca, B. and Bonačić-Kouteck{\´y}, Vlasta and Fantucci, P.}, title = {Ab Initio Adiabatic Dynamics Combined with Wigner Distribution Approach to Femtosecond Pump-Probe Negative Ion to Neutral to Positive Ion (NeNePo) Spectroscopy of Ag2Au, Ag4, and Au4 Clusters}, series = {Journal of Physical Chemistry A}, volume = {105}, journal = {Journal of Physical Chemistry A}, number = {39}, pages = {8892 -- 8905}, year = {2001}, abstract = {Ultrafast ground state nuclear dynamics of small coinage metal clusters is theoretically explored in the framework of negative ion to neutral to positive ion (NeNePo) femtosecond pump-probe spectroscopy with the aim to determine the scope and perspective of this technique. This approach involves the preparation of an initial ensemble in the anionic ground state of the cluster, one-photon detachment by the pump pulse, the propagation of the system on the neutral electronic ground state, and detection via the cationic ground state by a time-delayed ionizing probe pulse. The calculations of the NeNePo-ZEKE signals under the condition of zero kinetic energy electrons are based on the combination of the Wigner distribution approach and ab initio molecular dynamics (MD) "on the fly" in the framework of gradient-corrected DFT for the propagation of an ensemble of classical trajectories and involves the average over the entire phase space. We have chosen examples of Ag2Au and Au4 to investigate time scales and the character of isomerization processes that are influenced by a local minimum corresponding to an energetically high-lying isomer with the structure related to the initial anionic structure. Capture of the nuclei within the local minimum takes place with dephased (Ag2Au) or nondephased (Au4) vibrational relaxation. Structural relaxations leading to isomerization processes are in both cases of delocalized nature and take place after 1 ps. In contrast, the Ag4 cluster represents an example for which isomerization processes do not occur, since rhombic structures with slightly different bond lengths are global minima of the anionic and neutral ground states. Therefore, the relaxation dynamics is characterized by regular oscillations, which serve as fingerprints of structural properties. On the basis of the analysis of pump-probe signals and underlying dynamics, this contribution provides information about conditions under which structural properties of gas-phase clusters (global and local minima) and isomerization processes can be observed in the framework of the NeNePo-ZEKE type of spectroscopy. The latter is important in the context of applicability of this technique to the investigation of cluster reactivity.}, language = {en} } @article{BonačićKouteckyHartmannPittner2001, author = {Bonačić-Kouteck{\´y}, Vlasta and Hartmann, Michael and Pittner, Jiř{\i}́}, title = {Theoretical exploration of ultrafast spectroscopy of small clusters}, series = {The European Physical Journal D}, volume = {16}, journal = {The European Physical Journal D}, url = {http://nbn-resolving.de/urn:nbn:de:0298-opus4-5536}, pages = {133 -- 138}, year = {2001}, abstract = {We present the ultrafast multistate nuclear dynamics involving adiabatic and nonadiabatic excited states of non-stoichiometric halide deficient clusters (NanF) characterized by strong ionic bonding and one-excess electron for which the "frozen ionic bonds" approximation has been justified allowing to consider the optical response of the single excess electron in the effective field of the other electrons. We combined the Wigner-Moyal representation of the vibronic density matrix with the ab initio multi state molecular dynamics in the ground and excited electronic states including the nonadiabatic couplings calculated "on the fly" at low computational demand. This method allows the simulation of femtosecond pump-probe and pump-dump signals based on an analytical formulation, which utilizes temperature dependent ground state initial conditions, an ensemble of trajectories carried out on the electronic excited state as well as on the ground state after the passage through the conical intersection in the case of nonadiabatic dynamics and for probing either in the cationic state or in the ground state. The choice of the systems we presented has been made in order to determine the timescales of the fast geometric relaxation leaving the bonding frame intact as during the dynamics in the first excited state of Na4F3, and of the bond breaking processes leading to conical intersection between the first excited state and the ground state as in Na3F2. The former is the smallest finite system prototype for an surface F-center of bulk color centers. The latter allows to study the photo isomerization in full complexity taking into account all degrees of freedom. In the case of Na4F3 after the fast geometric relaxation in the excited state leading to deformed cuboidal structure without breaking of bonds, different types of internal vibrational redistribution (IVR) processes have been identified in pump-dump signals by tuning the dump laser. In contrast, from the analysis of the pump-probe signals of Na3F2 cluster, the timescales for the metallic and the ionic bond breaking, as well as for the passage through conical intersection have been determined. Finally the conditions under which these processes can be experimentally observed have been identified.}, language = {en} } @article{HartmannMitrićStancaetal.2001, author = {Hartmann, Michael and Mitrić, Roland and Stanca, B. and Bonačić-Kouteck{\´y}, Vlasta}, title = {Theoretical investigation of the ultrafast NeNePo spectroscopy of Au4 and Ag4 Clusters}, series = {The European Physical Journal D}, volume = {16}, journal = {The European Physical Journal D}, url = {http://nbn-resolving.de/urn:nbn:de:0298-opus4-5542}, pages = {151 -- 155}, year = {2001}, abstract = {Ultrafast ground state nuclear dynamics of Au4 and Ag4 is theoretically explored in the framework of negative ion - to neutral - to positive ion (NeNePo) pump-probe spectroscopy based on the ab initio Wigner distribution approach. This involves the preparation of a nonequilibrium neutral ensemble by pump induced photodetachment of a thermal anionic ground state distribution, gradient corrected DFT classical trajectory simulations "on the fly" on the neutral ground state, and detection of the relaxation process of the ensemble in the cationic ground state by a time-delayed probe pulse. In Au4, the initially prepared linear structure is close to a local minimum of the neutral state giving rise to characteristic vibrations in the signals for probe wavelength near the initial Franck-Condon transition. A timescale of ~1 ps for the structural relaxation towards the stable rhombic D neutral isomer was determined by the increase of the signal for probe wavelength in vicinity of the vertical ionization energy of the rhombic structure. In contrast, the relaxation dynamics in Ag4 is characterized by normal mode vibrations since both the initially prepared anionic ground state and the neutral ground state have rhombic minimum geometries. Thus, time-resolved oscillations of pump-probe signals are fingerprints of structural behaviour which can be used experimentally for the identification of particular isomers in the framework of NeNePo spectroscopy.}, language = {en} } @article{HartmannPittnerBonačićKoutecky2001, author = {Hartmann, Michael and Pittner, Jiř{\i}́ and Bonačić-Kouteck{\´y}, Vlasta}, title = {Ab initio nonadiabatic dynamics involving conical intersection combined with Wigner distribution approach to ultrafast spectroscopy illustrated on Na3F2 cluster}, series = {The Journal of Chemical Physics}, volume = {114}, journal = {The Journal of Chemical Physics}, number = {5}, pages = {2123 -- 2136}, year = {2001}, abstract = {We present a theoretical study of a femtosecond photo isomerization process due to a nonadiabatic radiationless decay from the first excited state through a conical intersection occurring in one of the nonstoichiometric halide-deficient clusters with one excess electron (Na3F2). This is an extension of the adiabatic dynamics study presented in the accompanying paper [J. Chem. Phys. 114, 2106 (2001)] for other members of the NanFn-1 series characterized by a strong ionic bonding for which the "frozen ionic bonds" approximation has been justified, allowing consideration of the optical response of the single excess electron in the effective field of the other electrons. In this contribution we outline the extension of the ab initio Wigner-distribution approach to nonadiabatic molecular dynamics which combines the Wigner-Moyal representation of the vibronic density matrix with the ab initio multistate molecular dynamics in the ground- and excited electronic states including the nonadiabatic coupling computed "on the fly" in connection with the fewest-switches hopping algorithm. This scheme allows accounting for temperature-dependent initial conditions, for the propagation in the excited state and in the ground state after the passage through the conical intersection, and for probing in the cationic ground state as well as for deriving analytic expressions for the pump-probe signals which utilize an ensemble of classical trajectories obtained at low computational demand. Our approach permits investigation of the photo isomerization through the conical intersection due to the long amplitude motion in the Na3F2 system in full complexity, taking into account all degrees of freedom. After breaking of one metallic and of one ionic bond the conical intersection occurs at the linear geometry and involves states of different symmetry which differ in the translocation of the one excess electron or positive charge localized at the Na atom from one end to the other of the system and separates two isomers with Cs and C2v structures. From the analysis of the nonadiabaticdynamics, the time scales for the metallic bond breaking of ∼90 fs and for the ionic bond breaking of ∼220 fs, for the passage through the conical intersection after ∼0.4 ps and for the internal vibrational energy redistribution (IVR) of more than 0.9 ps for the individual isomers, have been determined. The simulated fs pump-probe signals confirm the above results and provide the information about the experimental conditions such as laser frequencies and pulse duration under which bond breaking of different type as well as the population of each of the two isomers after the passage through the conical intersection can be identified. In this contribution we show that the mechanism of the photo isomerization at a conical intersection due to a long amplitude motion can occur in atomic clusters and is not necessarily limited to organic photochemistry.}, language = {en} } @article{HartmannPittnerBonačićKoutecky2001, author = {Hartmann, Michael and Pittner, Jiř{\i}́ and Bonačić-Kouteck{\´y}, Vlasta}, title = {Ab initio adiabatic dynamics involving excited states combined with Wigner distribution approach to ultrafast spectroscopy illustrated on alkali halide clusters}, series = {The Journal of Chemical Physics}, volume = {114}, journal = {The Journal of Chemical Physics}, number = {5}, pages = {2106 -- 2122}, year = {2001}, abstract = {We investigate the ultrafast multistate nuclear dynamics involving adiabatic electronic excited states of nonstoichiometric halide deficient clusters (NanFn-1) characterized by strong ionic bonding and one excess electron, which is localized either in the halide vacancy or on the alkali atom attached to the ionic subunit depending on the cluster size. For this purpose we developed an ab initio adiabatic nuclear dynamics approach in electronic excited and ground states "on the fly" at low computational demand by introducing the "frozen ionic bonds" approximation, which yields an accurate description of excited states considering the excitation of the one excess electron in the effective field of the other n-1 valence electrons involved in the ionic bonding. We combined this multistate dynamics approach with the Wigner-Moyal representation of the vibronic density matrix forming the ab initio Wigner distribution approach to adiabatic dynamics. This method allows the simulation of femtosecondNeExPo-pump-probe and NeExNe-pump-dump signals based on an analytic formulation which utilizes temperature-dependent ground-state initial conditions (Ne), an ensemble of trajectories carried out on the electronic excited state (Ex) for the investigation of the dynamics of the system, and either the cationic (Po) or the ground state (Ne) for the probing step. The choice of the systems has been made in order to determine the time scales of processes involving (i) metallic bond breaking such as during the dynamics in the first excited state of Na2F, and (ii) fast geometric relaxation leaving the bonding frame intact as during the dynamics in the first excited state of Na4F3. The bond-breaking process via a conical intersection involving nonadiabatic dynamics will be presented in the accompanying paper [Hartmann et al., J. Chem. Phys. 114, 2123 (2001)]. The dynamics in the first excited state of Na2F from triangular-to linear-to triangular structure gives rise to fast geometric relaxation due to Na-Na bond breaking at the time scale of ∼90 fs but no signature of internal vibrational energy redistribution (IVR) is present in NeExNe-pump-dump signals since the broken metallic bond prevents the coupling between stretching and bending modes. Instead, anharmonicities of the bending periodic motion have been identified. In contrast, in the case of Na4F3, which is the smallest finite system for a surface F-center prototype of bulk color centers, after the geometric relaxation in the excited state of ∼100 fs leading to the deformed cuboidal type of structure without breaking of bonds, different types of IVR have been identified in NeExNe signals by tuning the dump laser: one-mode selective energy leaving IVR, resonant, and restricted energy arriving IVR corresponding to the selection of different parts of the phase space. Dissipative IVR could not be identified in NeExNe signals of Na4F3 at low initial temperature on the time scale up to 2 ps in spite of 15 degrees of freedom. Due to similar structural and electronic properties such as F centers in bulk, these findings can serve as guidance for establishing the time scales for geometric relaxation and IVR in excited states of larger systems.}, language = {en} }