Ti 12 C 68 : A stable T h -symmetry hollow cage.

A stable T h -symmetry Ti12 C68 cage was systemically investigated using density functional theory. The structure of Ti12 C68 is a hollow cage with twelve TiC13 subunit of three pentagons and one hexagon. The calculated frequencies are in the range 95.1 cm-1 -1423.9 cm-1 . There are no imaginary frequencies, showing its kinetic stability. Ab initio molecular dynamics simulations demonstrate that the topological structure of cage-like Ti12 C68 cluster was well maintained when the effective temperature is up to 1139 K. The natural bond orbitals analysis shows that the d orbit of Ti atoms form four σ bonds with the neighboring four carbon atoms in each TiC13 subunit playing an important role in the cluster stability. The molecular frontier orbitals analysis indicates that Ti12 C68 cage has a narrow HOMO-LUMO gap with metal-like property. It would be expected to enrich the species of hollow metal carbide clusters.