Density Functional Investigation of Structural, Electronic and Spectral Properties of the HmTiSin (m=1∼2; n=2∼8) Clusters

In recent years, the silicon semiconductor clusters have experimentally and theoretically attracted great attention because of their potential applications regarded as cluster-assembled optoelectronic materials. Especially, the appropriate transition-metal atoms can stabilize the silicon clusters by doping to the surface of clusters, accordingly novel physical and chemical properties of transition-metal doped silicon clusters will be produced, e.g., optical property, magnetic property, and super-conductor, etc. In this work, the geometric structures and electronic properties of HmTiSin (m=1 similar to 2; n=2 similar to 8) clusters are systematically studied using the density functional theory (DFT) B3LYP method, and the changing regularity, dissociation channels and HOMO-LUMO gaps of the ground-state structures of the TiSin (n=2 similar to 8) clusters and their hydrides are discussed in detail. The results show that the Ti atom in the TiSin (n=2 similar to 8) clusters will gradually move from convex to surface and to interior sites along with the increasing number of the Si atom. For most of hydrogenated HmTiSin clusters, their stable structures keep the structural framework of TiSin clusters, while the H atoms prefer energetically to be attached on the silicon atoms, rather than the Ti atom. The analysis of dissociation energies as well as HOMO-LUMO gaps show that the adsorption of two H atoms on clusters' surfaces will eliminate the number of dangling bonds in these clusters, and largely improve the structural stability of clusters. The second-order energy differences (Delta E-2) can explore the chemical stability of the magic clusters, and it is found that the Delta E-2 is very sensitive to the cluster size, and has the local oscillation behaviors along with the increasing cluster size, in which the TiSi2 and TiSi6 clusters possess relatively higher stabilities than their neighboring ones, whereas the hydrogenated H1TiSi7 and H2TiSi7 clusters are the most stable in all of clusters studied here. In addition, we simulate the infrared spectra of these hydrogenated clusters, and assign the main vibrational peaks for further experimental references. These studies will provide significant theoretical references for further experimental synthesis and measurements of the transition metal-doped silicon based nanomaterials.