Large-scale Bethe-Salpeter equation calculations of core-level x-ray spectra

Recently an approach has been developed for Bethe-Salpeter equation (BSE) calculations of core-level x-ray spectra, which is implemented in the \textsc{ocean} package \footnote{ J. Vinson, E. L. Shirley, J. J. Rehr, and J. J. Kas, Phys. Rev. B {\bf 83}, 115106 (2011); J. Vinson and J. J. Rehr, Phys. Rev. B (in press , 2012)} which combines plane-wave, pseudopotential DFT electronic structure, PAW transition elements, GW self-energy corrections, and the NIST BSE solver. The method yields both dipole limited and finite momentum transfer spectra. Here we discuss several recent advances which yield a unified treatment of both extended states and atomic multiplet effects. In particular our approach now includes spin-dependent potentials and hole-dependent lifetimes, and gives an improved treatment of L$_{2,3}$ edges, where contributions to spectral weight come from a mix of two distinct core holes. We have also extended the code interface to include pseudopotential wave functions from \textsc{abinit}, \textsc{QuantumEspresso}, or an interpolation based scheme, thus enabling large-scale calculations with unit cells in excess of 2000 \AA$^3$. Applications to water and ice structures are briefly discussed.