ELECTRONIC-STRUCTURE AND BONDING IN THE METALLOCARBOHEDRENE TI8C12

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 cluster full-potential linear muffin-tin orbital method which is suited to arbitrary geometries and permits direct evaluation of the forces. As in the C60 molecule, the atoms form a spherical graphitelike shell with a threefold coordination at all sites. The calculated C-C and Ti-C bond lengths are 2.63 and 3.76 bohrs: the binding energy is 6.6 eV per atom. The bonding mechanism is quite different from that of the graphite crystal or the C60 molecule.