ELECTRONIC STATES OF C-60 MOLECULE ON SI(001)2X1 SURFACE

Electronic states are calculated by the DV-Xalpha-LCAO method for two model clusters C60Si57H44 and C60Si41H36 of the C60/Si(001) surface, where the C60 molecule resides on four and two Si dimers, respectively. Due to the electron transfer from the Si surface, the C60 molecule of the former (latter) cluster has ionicity -2.44 (-1.96). The highest occupied molecular orbital (HOMO) of the C60 molecule of the former cluster is lower than that of the latter cluster. This implies that the C60 molecule of the former cluster is more stable than that of the latter cluster. For both clusters, occupied (unoccupied) orbitals of the C60 molecule near the HOMO have high charge density around double bonds between two hexagons (around single bonds on pentagons). The charge density of an orbital has 4 or more stripes which should be compared with the scanning tunneling microscopy images.