DENSITY-FUNCTIONAL PSEUDOPOTENTIAL STUDY OF THE ENDOHEDRAL COMPLEX LI-2-AT-C-60

The spherically averaged pseudopotential (SAPS) model for treating the electronic structure and the energetics of a cluster of atoms is exte nded to allow use of first principles norm-conserving pseudopotentials including some nonlocality. The main theoretical development is the s pherical average about the chosen cluster centre of an s-wave projecti on operator associated with an off-centre ion which results in an addi tional radially nonlocal term in the radial Schrodinger equation, Howe ver, much of the simplicity of the SAPS model is preserved. The approa ch is used to study the electronic structure and the energetics of Li- 2@C-60. Self-consistent electron densities are obtained for the spheri cally averaged pseudopotentials corresponding to this endohedral compl ex and its component Li-2 and C-60 parts. The atoms are then allowed t o relax their positions to minimize the total energy. In the cases of Li-2 and C-60 considerable improvement is achieved over calculations u sing the SAPS model with local pseudopotentials. Two minimum energy co nfigurations are found for the Li-2 encapsulated inside a C-60 molecul e. That with the longer Li-Li bond length is the higher in energy by 0 .88 eV and is marked by almost complete charge transfer from the Li-2 to the C-60 cage. The other more stable isomer shows little charge tra nsfer but there is a noticeable build up of charge between the Li-2 an d the C-60.