Molecular-dynamics simulations of non-adiabatic processes at surfaces

Abstract

Time-dependent density functional theory, together with the adiabatic approximation for the time-dependent exchange-correlation potential, is combined with Ehrenfest dynamics for the nuclear motion to numerically simulate electronically non-adiabatic processes at surfaces. We have applied this method to electron–hole pair excitation at Al(111) surfaces evoked by the chemisorption of hydrogen atoms, a process which has been demonstrated experimentally by Nienhaus, McFarland et al. by measuring the induced chemicurrent, as well as the excitation of Si(001) surface atom vibrations induced by intense fs laser pulses. The simulations allow a detailed analysis of the non-adiabatic contribution to the Ehrenfest force acting on the atoms, the energy dissipation and the electron–hole excitation spectrum after a given simulation period. Due to the huge computational effort, the simulations are currently limited to a few hundred fs.