Making sense of the conflicting magic numbers in WSi(n) clusters

First principles studies on the geometric structure, stability, and electronic structure of WSi(n) clusters, n = 6-16, have been carried out to show that the observed differing "magic sizes" for WSi(n) clusters are associated with the nature of the growth processes. The WSi12 cluster, observed as a magic species in experiments reacting transition metal ions with silane, is not stable due to a filled shell of 18 electrons, as previously proposed, but due to its atomic structure that arrests further growth because of an endohedral transition metal site. In fact, it is found that all of these clusters, n = 6-16, have filled 5d shells except for WSi12, which has a 5d(8) configuration that is caused by crystal field splitting. The stability of WSi15 (+), observed as highly stable in clusters generated by vaporizing silicon and metal carbonyls, is shown to be associated with a combination of geometric and electronic features. The findings are compared with previous results on CrSi(n) clusters.