Stabilization of Si-based cage clusters and nanotubes by encapsulation of transition metal atoms

The encapsulation of metal atoms within Si-based cage clusters leads to stable metal-encapsulated Si cage clusters (Si-cc). The present work investigates the effect of encapsulation of transition metal atoms (TMAs). We show that the filling factor of the d-band of the TMA is the dominant factor determining the structural configuration of the Si-cc. This results in a contrasting bonding and magnetic behaviour of the endohedral Ni and V atoms. The size of the encapsulated atom is found to play a minor role. Both Ni and V were found to stabilize Si-cc. More significantly, we show that both Ni and V, in the form of one-dimensional chains, can stabilize Si nanotubes encapsulating the Ni or the V chain. Our results also show that these metal-encapsulated Si nanotubes have small conduction gaps and become metallic at infinite length.