Theoretical study of isoelectronicSinMclusters (M=Sc−,Ti,V+;n=14–18)
Physical Review B
We study, from first-principles quantum mechanical calculations, the structural and electronic properties of several low-lying energy equilibrium structures of isoelectronic Si n M clusters ͑M =Sc − ,Ti,V + ͒ for n = 14-18. The main result is that those clusters with n = 16 are more stable than its neighbors, in agreement with recent experimental mass spectra. By analyzing the orbital charge distribution and the partial orbital density of states, that special stability is rationalized as a
... ionalized as a combination of geometrical ͑near spherical cagelike structure for n =16͒ and electronic effects ͑l-selection rule of the spherical potential model͒. The structures of the two lowest energy isomers of Si 16 M are nearly degenerate, and consist of the Frank-Kasper polyhedron and a distortion of that polyhedron. The first structure is the ground state for M =V + , and the second is the ground state for Ti and Sc − . For the lowest energy isomers of clusters Si n M with n = 14-18, we analyze the changes with size n, and impurity M of several quantities: binding energy, second difference of total energy, HOMO-LUMO gap, adiabatic electron affinity, addition energy of a Si atom, and addition energy of an M impurity to a pure Si n cluster. We obtain good agreement with available measured adiabatic electron affinities for Si n Ti.