Practical, reliable, and large-scale calculations of x-ray spectra using the Bethe-Salpeter equation method

First-principles calculations of x-ray absorption spectra are widely used to help interpret and understand measured spectra. However, their broad adoption is held back in part by unfamiliarity with available codes, perceived computational cost, and uncertainty about the accuracy of calculations. In this talk I will discuss the Bethe-Salpeter equation (BSE) approach to spectroscopy within the context of other available methods. I will introduce the OCEAN code and some of the recent advances that have made it more accurate, easier to use, and more efficient. I will then highlight examples where the BSE method successfully reproduces measured spectra and what that tells us about the underlying electronic structure of the materials. I will end by discussing some of the challenges in assessing the accuracy of theoretical x-ray methods and recent work on establishing quantitative comparisons between different codes and methods.