Ehrenfest molecular dynamics approach to a light-induced softening of aluminum slab based on time-dependent density functional theory

Modulation in lattice kinetics of simple metals under the irradiation of an ultra-short laser pulse is of great interest to both industrial applications and fundamental physics. In our study we performed Ehrenfest molecular dynamics (Ehrenfest MD) simulation of a nine-atomic-layer-thick aluminum slab based on time-dependent density functional approach. In our simulation the slab has (111) surface of aluminum fcc structure. The slab is put in vacuum, and is exposed to a femtosecond laser pulse. To analyze the Ehrenfest MD results, we employed a quasi one-dimensional model that bounds neighboring layers by a quadratic potential. Model parameters are fitted so that they reproduce Ehrenfest MD trajectory. We found a significant and non-uniform reduction of the force constants with the increase of laser intensity suggesting lattice softening by electronic excitation. In this presentation, we compare the results with the case of Born-Oppenheimer MD under finite electron temperature and discuss the correspondence between these two distinct types of theoretical methods.