Comparison of physical processes of atom-surface scattering computed by classical and quantum dynamics

TL;DR

This study compares classical and quantum simulations of atom-surface scattering, revealing differences in energy loss, escape probability, and angular distribution, with quantum effects being significant at low energies.

Contribution

It introduces a combined classical-quantum simulation approach for atom-surface scattering and highlights quantum effects at low incident energies.

Findings

Quantum energy loss is smaller than classical at low energies.

Classical escape probability increases with temperature, quantum remains nearly constant.

Angular distributions differ qualitatively between classical and quantum simulations.

Abstract

We have performed classical and quantum dynamical simulations to calculate dynamical quantities for physical processes of atom - surface scattering, e.g., trapping probability and average energy loss, final angular distribution of a particle scattered from a corrugated thermal surface. Here we have restricted ourselves to in-plane scattering so that only two degrees of freedom of the particle have to be considered - the vertical distance z and the horizontal coordinate x. Moreover, we assumed further that only the vertical coordinate fluctuates due to interaction with thermal phonon bath of the surface. Initial phase - space variables of the system and the bath for our classical simulations were generated according to Wigner distribution functions which were derived from initial wavefunctions of our quantum dynamics. At very low incident energy, we have found that the quantum mechanical average energy loss of the escaped particle from the corrugated as well as thermal surface are smaller than the classical ones at a particular surface temperature. It is important to note that the rate of escaping probability of the scattered particle obtained by classical simulation increases with increasing surface temperature. On the other hand, quantum rate is almost temperature independent at 2 meV incident energy of the particle, whereas it shows same trend with the classical results at 5 meV and the quantum rate is lower than the classical rate. We have also noticed that the final angular distributions of the scattered particle both for classical as well as quantum dynamics are qualitatively different but the quantities are more or less temperature independent.