X-ray-absorption study of rhenium ${\mathit{L}}_3$ and ${\mathit{L}}_1$ edges in ${\mathrm{ReO}}_3$: Multiple-scattering approach

We present ab initio calculations of x-ray-absorption fine structure for the Re ${\mathit{L}}_3$ and ${\mathit{L}}_1$ edges in crystalline ${\mathrm{ReO}}_3$ based on an exact curved-wave multiple-scattering approach. Good agreement between theoretical and experimental data has been found for both edges. We show that (1) as expected, the contribution of multiple-scattering signals from linear chains, like Re-O-Re and O-Re-O, is very large both in the ${\mathit{L}}_3$- and ${\mathit{L}}_1$-edge spectra due to the strong focusing effect caused by the middle atom; (2) the additional difference between two edges, besides the one in central-atom phase shifts and the π factor, originates from the geometrical dependence of multiple-scattering terms on the final l state, especially for paths forming a right angle at the absorbing atom; (3) the fine structure above the ${\mathit{L}}_1$ edge is a superposition of two signals from ${\mathit{L}}_1$ and ${\mathit{L}}_2$ edges with a very significant contribution of the latter.