Orbital ordering, Jahn-Teller distortion, and anomalous x-ray scattering in manganates

We demonstrate with LSDA + U calculations that x-ray scattering at the K ed ge of Mn is sensitive to orbital ordering in one energy range and Jahn-Tell er distortion in another. Contrary to what is suggested by atomic or cluste r models used to date we show that band structure effects rather than local Coulomb interactions dominate the polarization dependence of the K edge sc attering and therefore it is sensitive to nearest neighbor bond length dist ortions and next nearest neighbor orbital occupation. Based on this we prop ose a new mechanism for K edge x-ray scattering in the manganates which we suggest is also applicable to transition metal compounds in general. [S0031 -9007(99)09199-1].