The quantitative applicability of a sub-space optimization method, formulated in terms of localized non-orthogonal orbitals, was investigated. A Grassmann conjugate gradient algorithm was the sub-space optimization method. The substitution of a Si atom by a N atom in cubic SiC with 2 different configurations was used as a test system. Modifications of the existing method were made for the inclusion of a half-filled defect level. The approximation of localization for the orbitals gives linear scaling of the dominant parts of the algorithm thus allowing for the simulation of large systems. Numerical tests indicated that quite accurate quantitative results were obtained when using extended orbitals near the defect and a localization regions with radii of 7 Bohr for orbitals away from the defect.

Applicability of O(N)-Like Density Functional Study on the Structural Properties of Nitrogen Defects in SiC. D.Raczkowski, C.Y.Fong: Physical Review B, 2003, 68[1], 014116 (5pp)