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 hex agonal graphite. Our results show asymmetry similar to the experimenta l and previous pseudopotential calculations. The dominant feature is t he deep hollow in the middle of the carbon hexagon. The three carbon a toms that do not have a neighbor in the second layer appear as small h ills, the other three with neighbors in the second layer simply appear as saddle points. Our calculation has been successfully used to repro duce experimental features such as the effect of increasing the magnit ude of the bias voltage and the effect of increasing the tip-to-surfac e separation.