Stengel M, Vita AD, Baldereschi A

The irreversible (6x6) reconstruction of the C-60/Al(111) system from the (2root3x2root3)R30degrees phase is studied by first-principles techniques. We find that C-60 binds optimally to the surface if an Al vacancy is created directly underneath. The removed Al atoms form a (6x6) array of ad-dimers in the interstices below the C-60 overlayer, to which they strongly bind. This spontaneous local process, rather than the compression state of the unreconstructed C-60 overlayer, explains why one molecule out of three protrudes from the surface upon reconstruction.