A technique for relativistic spin-polarised calculations

A technique for reduction of the Dirac equation, which initially omits the spin-orbit interaction (thus keeping spin as a good quantum number), but retains all other relativistic kinematic effects such as mass-velocity, Darwin, and higher order terms is presented. The spin-orbit interaction can be included as a perturbation once the 'relativistic' spin-polarised bands and wavefunctions have been obtained. The technique is used together with the local spin density approximation for exchange and correlation to calculate the self-consistent charge and spin density of a neutral Gd atom. The calculated magnetic form factor agrees extremely well with experiment. Comparison with a paramagnetic RAPW calculation shows the procedure should be accurate and fast for general band structure determinations.