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

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