XANES calculation with an efficient ``Non Muffin-Tin'' method: Application to the angular dependence of the AlK-edge in corundum

We present a reciprocal-space ``non mufin-tin'' scheme for calculating X-ray Absorption Near-Edge Structure (XANES). The method uses pseudopotentials and reconstructs all electron wave functions within the Projector Augmented Wave framework. The method incorporates a recursive method to compute absorption cross section as a continued fraction. The continued fraction formulation of absorption is advantageous in that it permits the treatment of core-hole-electron interaction through large supercells ( hundreds of atoms). This opens new fields of applications like surfaces, molecules, small aggregates or amorphous materials, for which large supercells are required. The method is applied to the natural linear dichroism at the Al K-edge in corundum (alpha-Al2O3). Details about the convergence process of the calculation are given. The influence of the core-hole effects is emphasized and comparison with ``muffin-tin'' multiple scattering calculation is made