An orthogonalized valence orbital approximation in relativistic full-potential linear-combination-of-atomic-orbitals methods

An approximation for reducing the computational cost in fully relativistic and scalar relativistic full-potential linear-combination-of-atomic-orbitals (LCAO) methods is introduced. The basic idea is the same as in the orthogonalized plane wave method; valence orbitals are orthogonalized to core orbitals and, using the orthogonalized valence orbitals as the basis functions in the generalized eigenvalue problem, the size of matrices is reduced considerably for materials with heavy atoms. This enables us to calculate their structural and electronic properties efficiently. The usefulness of the orthogonalized valence orbital approximation is shown by applying it to An, InSb, and AmBi. In particular, it is found that the effect of spin-orbit coupling is reproduced successfully in the fully relativistic full-potential LCAO calculations within the orthogonalized valence orbital approximation.