Stability of alkali-encapsulating silicon cage clusters

We report a computational study of the possibility to form alkali-encapsulating Si clusters A@Si(n) with n = 10 - 20. We predict and quantify the stability for lithium, sodium, and potassium atoms encapsulated in silicon cage. The structure and electronic properties are discussed. An electronic charge transfer from the alkali atom to the Si(n) cage is observed. The A@Si(n) cluster is formed of a positive charge located on the alkali surrounded by a negative one distributed on the whole Si cage. For each size the predicted stability of such structure is discussed and compared with that of surface-bound alkali isomers. The alkali-encapsulating Si clusters A@Si(n) are found to be stable but lying much higher in energy as compared to surface-bound alkali isomers.