Molecular dynamics simulations of sodium nanoparticle deposition on magnesium oxide

The interaction of mass-selected atomic clusters and nanoparticles with surfaces attracts strong interest in view of fundamen- tal research and technological applications. Understanding the 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 experi- mentally relevant magnesium oxide substrate is studied by means of classical molecular dynamics simulations. An empiri- cal 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.