X-ray absorption near edge structure calculation beyond the muffin-tin approximation

A new scheme of calculation for X-ray Absorption Near Edge Structure (XANES) based on the finite-difference method is proposed. It permits a potential shape completely free and in particular not constrained in the muffin-tin approximation. In our approach, the calculation of the final states is performed in real space. The spherical areas around the atomic nuclei art reduced to very small spheres where the approximation is in any case valid. Between the spheres, the Schrodinger equation is solved in a discrete form on the node points of a three-dimensional grid. The unknowns are the values of the wave function at the grid points. Results on oxides show good agreement between experiment and theory. This procedure can give access to new parameters such as the charge exchange between atoms.