First-principles calculations were made of positron lifetimes at various vacancies. Lattice relaxations and electron redistributions, caused by the vacancy and the positron, were included by using 2-component density-functional theory. The calculated lifetimes agreed with experimental data on mono-vacancies and di-vacancies, and previously measured longer lifetimes were attributed to stable multi-vacancies.

M.Saito, A.Oshiyama: Physical Review B, 1996, 53[12], 7810-4