  Molecular dynamics simulations of a Xe monolayer sliding on Ag(001) and
Ag(111) are carried out in order to ascertain the microscopic origin of
friction. For several values of the electronic contribution to the friction of
individual Xe atoms, the intra-overlayer phonon dissipation is calculated as a
function of the corrugation amplitude of the substrate potential, which is a
pertinent parameter to consider. Within the accuracy of the numerical results
and the uncertainty with which the values of the relevant parameters are known
at present, we conclude that electronic and phononic dissipation channels are
of similar importance. While phonon friction gives rise to the rapid variation
with coverage, the electronic friction provides a roughly coverage-independent
contribution to the overall sliding friction.
