Geometric and Electronic Structure of WSi_N(N = 1–6, 12) Clusters

Abstract

Geometry optimizations of WSi _N (n = 1–6, 12) clusters are performed using the B3LYP/ LanL2DZ method for a sequence of different spin states, changing from spin singlet to spin septet conditions. The resulting equilibrium structures are discussed under the aspects of geometric features, cluster internal charge transfer and magnetic properties. It is shown that the W impurity in the Si _N environment generally acts as an electron acceptor. However, the charge on the W atom, as obtained by natural population analysis, can be sensitively tuned through the variation of the spin constraint from S = 0 to S = 3. The resulting geometries of WSi _n (N = 3–6) are compared with the known ground state structures of Si _N+1 (N = 3–6), and substitutional geometries are identified for N = 3 and N = 5. The nonzero spin states of WSi _N are shown to display different patterns of magnetic order, corresponding to uniform and to alternating atomic spin orientations within the cluster. Highly compact O _h and D _6h structures are identified as stable geometries of WSi₆ and of the experimentally detected unit WSi₁₂, respectively. Comparison is made with the cluster series MoSi_N(N = 1–6) and CuSi _N (N = 1–6,12).