STRUCTURE OF SI60 - CAGE VERSUS NETWORK STRUCTURES

A generalized tight-binding molecular dynamics technique which was use d to obtain complete agreement with ab initio results for small silico n clusters is used to optimize the Si60 cage without any symmetry rest rictions. The perfect icosahedral cage is found to be unstable, distor ting to a lower symmetry C2h, Structure with no change in the threefol d coordination. The relaxed geometry shows increasing tendency for tet rahedral arrangement of atoms, and is energetically unfavorable compar ed to a relaxed bulk-like fragment. This is in contrast to carbon, whe re the cage is favored.