Spin-polarised relativistic electronic structure calculations

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Abstract
A fully relativistic first-principles electronic structure calculation method is presented for magnetic materials. The method is based on the local spin moment density concept for relativistic Hamiltonians. In order to obtain manageable Kohn-Sham-Dirac equations including magnetic fields, the orbital contribution to the four-current density is omitted. The starting point is Takeda's relativistic generalisation of the augmented spherical wave method for non-magnetic crystals (RASW). In its basic form, the proposed method for magnetic crystals is only slightly more involved as RASW, and still takes all relativistic and spin polarisation effects into account, from first principles (including the Delta l=2 coupling). The treatment of relativistic and spin polarisation effects can be called 'on equal footing'. In both relevant limits the method is exact (within the mentioned framework). Furthermore, a more elaborate scheme is suggested, which is a systematic improvement of the basic scheme. A comparison is made with other recently published methods. Finally, results of self-consistent calculations for ferromagnetic Ni and Gd, performed with the basic scheme, are compared with previous calculations and experimental data from the literature. For Ni, the results are in good agreement both with previous calculations and with experiment. For Gd interesting new results have been obtained concerning the spectroscopic splitting factor g. The influence of the choice for an explicit exchange and correlation functional is studied as well as the influence of the coupling between l and l+2 levels.

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