First principles calculations of Si doped fullerenes: Structural and electronic localization properties in C59Si and C58Si2

Si-doped heterofullerenes C59Si and C58Si2, obtained from C-60 by replacing one and two C atoms with Si atoms, are investigated via first principles c alculations. Static geometry optimizations show that structural deformation s occur in the vicinity of the dopant atoms and give rise to Si-C bonds sig nificantly larger than the ordinary C-C bonds of the fullerene cage. In the case of C58Si2, the lowest energy isomer has two Si atoms located at dista nces corresponding to third nearest neighbors. The electronic structure of these heterofullerenes, although globally close to that of C-60, is charact erized by a strong localization of both the HOMO's and the LUMO's on the Si sites. Charge transfer occurs from the dopant atoms to the nearest neighbo r C atoms, contributing to the formation of polar Si-C bonds. A detailed an alysis of the charge localization, based on the electron localization funct ion and maximally localized Wannier function approaches, reveals that the b onding of Si in the fullerene cage consists of two single and one weak doub le bond, thus preserving the conjugation pattern of the undoped C-60. Besid e the charge localization along the bonds, we observe a peculiar region of charge localization outside the cage above each Si atom. These features are discussed in comparison with the corresponding patterns exhibited by the C -60 system. (C) 1999 American Institute of Physics. [S0021-9606(99)30938-7] .