First-principles total-energy pseudopotential calculations were used to study the so-called negative-U large lattice relaxation model for column-III and VII donors. Three distinct types of DX-like structure, characterized by either bond rupture or bond compression, were found for column-VII donors. The relative stabilities of these structures were impurity- and pressure-dependent. All of the donor impurities gave deep centers.

C.H.Park, D.J.Chadi: Physical Review B, 1995, 52[16], 11884-90