Ab initio periodic Hartree-Fock calculations for interpretation of the scanning tunneling microscope (STM) images of graphite

By using the CRYSTAL95 program, ab initio periodic Hartree-Fock (PHF) calculations with the full potential and 6-21G* basis set are applied to interpretation of scanning tunneling microscope (STM) images on hexagonal graphite. Our results show asymmetry similar to the experimental and previous pseudopotential calculations. The dominant feature is the deep hollow in the middle of the carbon hexagon. The three carbon atoms that do not have a neighbor in the second layer appear as small hills, the other three with neighbors in the second layer simply appear as saddle points. Our calculation has been successfully used to reproduce experimental features such as the effect of increasing the magnitude of the bias voltage and the effect of increasing the tip-to-surface separation.