Calculations of electron energy loss and x-ray absorption spectra in periodic systems without a supercell

Ab initio calculations of relativistic core-level electron-energy-loss spectra and x-ray absorption spectra in periodic systems are carried out using an impurity Green's function formalism without the need for a supercell. The approach is based on a hybrid scheme incorporating a reciprocal space calculation of the multiple-scattering equations, together with a real-space calculation of the excitation spectrum with a statically screened core-hole potential. The approach accounts for core-hole effects in deep-core spectroscopies of periodic systems while circumventing the supercell convergence issues encountered with conventional band-structure codes. The approach is implemented in an extension of the real-space Green's function code FEFF. Illustrative calculations are presented for the K edges of C (diamond) and Cu, and the N K edge of GaN.