Ab initio calculations were used to investigate the structural and electronic properties of vacancies in SixGe1–x. The (++), (+), (0), and (–) charge states were studied and the substitutional disorder of the alloy was considered explicitly. A linear relationship was found between the effective-U for the system formed by the (++), (+), and (0) charge states and the number of Si atoms in the first neighborhood of a vacancy (NSi). The effective-U was positive when NSi was zero, and it was negative when NSi was 2 and 4. In all cases, the absolute value of the effective-U in the alloy was significantly smaller than its value for pure Si and pure Ge.

Ab initio Calculations of Vacancies in SixGe1–x. G.M.Dalpian, P.Venezuela, A.J.R.da Silva, A.Fazzio: Applied Physics Letters, 2002, 81[18], 3383-5