Structure and Stability of TiBn (n=1-12) Clusters: An ab initio Investigation

Based on the density functional theoretical (DFT) BPBE and ab initio CCSD(T) calculations, the geometries and stabilities of TiBn (n=1-12) clusters have been systematically investigated. For BPBE calculations, the orbitals of B atoms are described by the 6-311+G(d) basis set, and that of Ti atom by CEP-121G basis set. For CCSD(T) calculations, CC-PVTZ basis set is applied for both B and Ti atoms. It is found that the most stable TiBn clusters can be constructed from the most stable Bn+1 clusters when n <= 6, except of TiB4, by replacing one B atom at the edge of the Bn+1 cluster with one Ti atom. With the increase of n, the TiBn clusters evolve from planar structure to three-dimensional structure. From TiB7 to TiB12, the most stable structure has nest-like structure. The calculated second-order difference of energies manifests that the magic numbers of stability are 2, 8 and 10 for the TiBn clusters in CCSD(T) level, which is different from the result of DFT calculations. Both BPBE and PW91 methods of DFT showed the magic numbers of stability are 3, 7 and 10. This difference implies the importance of electronic correlation in TiBn clusters. The vertical ionization potentials (VIP) and vertical electronic affinities (VEA) of TiBn clusters are reported at CCSD(T) level. The TiBn clusters with closed-shell electronic configuration have smaller VEA and greater VIP, which are more stable in the chemical reactivity view of point.