Electronic structures of C60 and C70 adsorbed on the Cu(111) surface and intramolecular STM images.

Abstract

Recent scanning tunneling microscopy (STM) experiments have revealed that ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ adsorbed on the Cu(111)-(1\ifmmode\times\else\texttimes\fi{}1) substrate show specific bias-voltage-dependent images that seem to reflect individual cage structures. In order to understand this experimental observation, band structures and partial charge-density distributions of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ are calculated by means of an all-electron mixed-basis approach. In this paper we adopt two-dimensional molecular models without substrates and proper orientational adsorption geometries of fullerenes. By comparing the calculated charge distributions of the lowest-unoccupied-molecular-orbital bands and the highest-occupied-molecular-orbital bands with the STM images, we find that the intramolecular patterns that change with the bias voltage strongly reflect the positions of five-membered and six-membered rings.