Self-consistency, spin-orbit and other advances in the FDMNES code to simulate XANES and RXD experiments

Abstract

A user friendly tool allowing the simulation of x-ray absorption near edge structure (XANES) spectra and Resonant X-ray Diffraction (RXD) peak intensity is necessary for many purposes. We present the actual developments of the FDMNES code which realizes this task in a mono-electronic approach. The code uses both the multiple-scattering theory and the finite different method in a fully relativistic frame, including thus the spin-orbit interaction. In diffraction, the resonant and non-resonant, magnetic and non-magnetic components are all included, allowing an easy use by non experts of the code. In the same idea, the automatic analysis of the unit cell (or molecule) symmetry greatly simplifies the user's work. Summation on and energy shift between the different absorption sites are automatically included. Comparison with experiment in order to fit parameters is also possible. The last advances with the self-consistent calculations are discussed. It is shown that within the multiple-scattering theory, using the muffin-tin approximation on the shape of the potential, the improvement is not high for non magnetic situation and limited to the pre-edge region. The improvements coming from the non-muffin-tin corrections are notably higher. More improvement results from self-consistency for the magnetic NdMg system. Various examples in oxides and metal in RXD and XANES are given showing the potentiality of the code. The fit procedure is applied in the magnetite low temperature phase case.