Electronic structure and bonding in the metallocarbohedreneTi8C12

Total-energy and electronic-structure calculations are presented for a recently proposed dodecahedral cluster of eight titanium and twelve carbon atoms. The calculations were done using density-functional theory and a recently developed cluster full-potential linear muffin-tin orbital method which is suited to arbitrary geometries and permits direct evaluation of the forces. As in the ${\mathrm{C}}_{60}$ molecule, the atoms form a spherical grahitelike shell with a threefold coordination at all sites. The C-C and Ti-C bond lenghts are calculated to be of 2.63 and 3.76 bohrs, respectively, and the binding energy is 6.6 eV per atom. The bonding mechanism is quite different from that which stabilizes the graphite crystal or the ${\mathrm{C}}_{60}$ molecule.