First-Principles Calculations of Scanning-Tunneling-Microscopy Images of Ar Atoms Adsorbed on a Graphite Sheet

Local density approximation in the framework of the density functional theory is applied to calculate the scanning tunneling microscopy (STM) images of Ar atoms adsorbed on a graphite sheet (Ar/graphite system). It is found that the optimal site of adsorbed Ar atom is at the top of the center of the carbon hexagon and its equilibrium distance from the graphite surface is about 3.20Å. We demonstrate that it is the hybridization of the C 2p electronic states with the Ar 3p and 4s electronic states, which renders Ar atoms visible in the STM experiment.