Some consequences of relativistic effects upon optical spectra

Large spin-orbit interaction produces large orbital magnetic moments in nar row energy bands. Since the orbital character of the wave functions is more important in orbital than in spin magnetism, the limitations of the local spin density approximation become evident. It is possible to keep the orbit al dependence of the exchange interactions by using an orbital polarization scheme or by using Hartree-Fock theory with screened Slater integrals for exchange. This leads to an enhancement of the calculated orbital moment whe n the magnetism is strong. Recently calculated magnetic moments and calcula ted sum rules for X-ray magnetic circular dichroism in US are described.