Modification of geometrical and electronic structures of anionic and neutral silicon clusters by double-doped tantalum atoms

Abstract

In this work, structural evolution, geometrical and electronic structures of Ta2Sin − and Ta2Sin (n = 3–21) clusters are investigated by joint Crystal structure AnaLYsis by Particle Swarm Optimisation (CALYPSO) global search algorithm and quantum chemical calculations. n = 21 is confirmed as the critical size of forming a Ta2-endohedral silicon cage-like structure for both anionic and neutral Ta2Sin clusters. It is found that the two Ta atoms tend to occupy the high coordination sites and stay close as a whole to bond with the Sin frames, as a result, the global minima of Ta2Sin − /0 (n = 3–21) clusters can be all viewed as a central Ta–Ta bonding axis interacted with the surrounding Si atoms. Ta2Sin − /0 (n = 3−13) clusters are majorly dominated by the bipyramid or prism-based geometries and Ta2Sin − /0 (n = 14−18) clusters are primarily governed by the polyhedral cage-like geometries, whereas Ta2Sin − /0 (n = 19−21) clusters are mainly controlled by the prolate geometries. In particular, Ta2Si3 − has a D 3h symmetric trigonal bipyramid structure, and Ta2Si6 − adopts C 2h symmetric chair-shaped structure and Ta2Si12 − is a C 6v symmetric Ta-face-capped hexagonal antiprism with the other Ta atom at the interior of Si12 cage. The odd-even alternations for the relative stabilities of Ta2Sin − /0 are observed.