First principles study of the adsorption of C-60 on Si(111)

The adsorption of C-60 on Si(1 1 1) has been studied by means of first-prin ciples density functional calculations. A 2 x 2 adatom surface reconstructi on was used to simulate the terraces of the 7 x 7 reconstruction. The struc ture of several possible adsorption configurations was optimized using the ab initio atomic forces, finding good candidates for two different adsorpti on states observed experimentally. While the C-60 molecule remains closely spherical, the silicon substrate appears quite soft, especially the adatoms , which move substantially to form extra C-Si bonds, at the expense of brea king Si-Si bonds. The structural relaxation has a much larger effect on the adsorption energies, which strongly depend on the adsorption configuration , than on the charge transfer. (C) 2001 Elsevier Science B.V. All rights re served.