Semi-classical electron dynamics in metal clusters beyond mean-field

We discuss the importance of dynamical correlations in the electronic respo nse of metal clusters to violent excitations. The theoretical description i s based on the Vlasov equation, the semi-classical variant of the time depe ndent local density approximation (TDLDA) to density functional theory (DFT ). Dynamical correlations are added by a quantum-kinetic collision term lea ding to the Vlasov-Uehling-Uhlenbeck (VUU) equation. As test cases we consi der excitations of sodium clusters either by a rapid collision with a highl y charged projectile or by intense femtosecond laser pulses. We find that t he collective response and direct ionization (following immediately the exc itation process) are insensitive to dynamical correlations for the case of short excitation processes (taking at most a few fs) where two-body collisi ons have no time to become active. For longer excitations, however, the VUU collision term plays an important role. Whatever the excitation time, dyna mical correlations, as described in VUU, are always playing a crucial role in the energy deposition mechanism and subsequent heating of the electron c loud. Such a phenomenon is thus likely to have strong impact on ionic motio n inside the cluster on even longer time scales. (C) 2000 Academic Press.