Relativistic short-range-order X-ray photoelectron diffraction theory

In this paper we discuss relativistic short-range-order XPD theory applicable to the XPD front heavy elements (Z > 50), where relativistic effects play some important roles. The 4 x 4 Dirac Green's function can be expanded in terms of full non-relativistic 2 x 2 Green's functions using Gestzesy expansion, which enables LIS to use well-defined Debye-Waller factors and optical potentials developed within the framework of nonrelativistic theory. We separately discuss the K-edge and other nonspherical deep core excitation by linear and circular polarized X-rays. The relativistic effects play a minor role in the analyses of K-edge XPD excited by linear polarized X-rays, whereas they play an important role in the analyses of spin-resolved K-edge XPD spectra excited by circularly polarized X-rays. Sonic illustrative numerical calculations demonstrate the contribution to spin polarization in the XPD spectra caused by the relativistic effects.