  The interaction of mass-selected atomic clusters and nanoparticles with
surfaces attracts strong interest in view of fundamental research and
technological applications. Understanding dynamics of the deposition process is
important for controlling structure and functioning of deposited nanoparticles
on a substrate, but experimental techniques can usually observe only the final
outcome of the deposition process. In this paper, the deposition of 4 nm-sized
sodium nanoparticles on an experimentally relevant magnesium oxide substrate is
studied by means of classical molecular dynamics simulations. An empirical
force field is derived which accounts for the interaction of highly polarizable
Na atoms with the surface, reproducing the results of previously reported
quantum mechanics/molecular mechanics simulations. Molecular dynamics
simulations permit exploring the dynamics of deposited nanoparticles on long
timescales on the order of hundreds of picoseconds, thus enabling the analysis
of energy relaxation mechanisms and the evolution of nanoparticle structure up
to its thermalization with the substrate. Several nanoparticle characteristics,
such as internal structure, contact angle, and aspect ratio are studied in a
broad deposition energy range from the soft landing to multi-fragmentation
regimes.
