On-site approximation for spin-orbit coupling in linear combination of atomic orbitals density functional methods

We propose a computational method that drastically simplifies the inclusion of the spin-orbit interaction in density functional theory when implemented over localized basis sets. Our method is based on a well-known procedure for obtaining pseudopotentials from atomic relativistic ab initio calculations and on an on-site approximation for the spin-orbit matrix elements. We have implemented the technique in the SIESTA (Soler J M et al 2002 J. Phys.: Condens. Matter 14 2745-79) code, and show that it provides accurate results for the overall band-structure and splittings of group IV and III-IV semiconductors as well as for 5d metals.