Impact of neglecting p-type spin-orbit coupling during electronic structure calculations on solids

Fully relativistic density functional theory electronic structure calculations for crystalline solids have become nearly commonplace. It has been demonstrated, however, that two of the more common methods used for such calculations produce spin-orbit coupling energies for p-type orbitals that are numerically unstable. The source of the instability and methods for its mitigation are discussed here. In particular, a stabilization strategy suggested by Soderlind, the complete neglect of p-type spin-orbit coupling, is tested for a prototypical p-bonded metal, Pb, using the linear combinations of Gaussian-type orbitals-fitting function method. The zero-pressure lattice constant and bulk modulus are both insensitive to the p-type spin-orbit coupling. The density of states and the fcc-bcc structural energy difference, however, are shown to be significantly affected by p-type spin-orbit coupling. The complete neglect of p-type spin-orbit coupling approximation should not be used to determine structural phase transition pressures for materials in which the bonding has a strong p character. (C) 2004 Wiley Periodicals, Inc.