Spin-orbit coupling in the actinide elements:: A critical evaluation of theoretical equilibrium volumes -: art. no. 035103

The difficulty of converging the contribution of the spin-orbit interaction to the total energy within an ls basis in actinide electronic structure calculations is discussed in detail. In particular, it is demonstrated that the source of the poor convergence is the treatment of the actinide 6p states. The limitation of the standard approach to relativity in full potential methods is manifested in muffin-tin based methods by a dependence of the total energy on the choice of muffin-tin radius. Despite this limitation it is found that structural phase stabilities are not affected, nor are pressure induced phase transitions. In order to treat the relativistic spin-orbit coupling in as large a part of space as possible one should, in muffin-tin based calculations, use a radius that is touching, or near touching, for all calculated volumes.