Theoretical Description of Ultrafast Structural Relaxation

The excitation of a molecule or cluster by an ultrashort laser pulse - as is shown for silver aggregates in Chap. 5 - induces time-dependent changes of their electronic and atomic structure. These changes can be nicely studied by real-time experiments inducing charge reversal processes (see the NeNePo scheme in Fig. 1.1). Very recently, several rather different theoretical approaches have been published or presented at conferences dealing with the relaxation mechanisms induced by ultrafast excitation processes. A brief summary of these theories is given here. 

Bennemann, Garcia, and coworkers [134, 135] described the ultrafast structural response of the optically excited Aga molecule by combining a microscopic electronic theory with molecular dynamics simulations in the 

Born-Oppenheimer approximation. In particular, they analyzed the time evolution of the ionization potential and the dependence of the dynamics on the initial temperature of the Aga molecule. The simulations were performed by use of the Verlet algorithm in its velocity form. 

Engel and coworkers [312] also investigated the time-resolved charge reversal process in molecules and applied their theory to the organometallic molecule ironcarbonyl (FeCO). A direct grid propagation of nuclear wave packets was used. Compared with [136], Engel states that the main purpose 

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