Invited Talk: Eric ShirleyOn electron spectroscopy using theory, x-ray absorption and resonant Auger techniques

A variety of theoretical methods treat electron excitation spectra (x-ray absorption, photoemission, Auger electron spectroscopy, or XAS, PES, AES). These include excited-state density-functional theory, the GW/Bethe-Salpeter (BSE) framework, real-space multiple-scattering methods, and the cumulant-based methodology meant to tackle satellites in spectra. Different methods treat different aspects and are also used in combination. This talk will feature a BSE-centered survey of work in many materials. We begin with the isoelectronic series: Ge, GaAs, ZnSe, CuBr; showcasing the successes and challenges of the BSE methodology, as well as a "chemical alchemy" effect borne out by standard extended x-ray absorption fine structure (EXAFS) analysis. The role of Debye-Waller effects is also of interest in these systems. We next turn to molybdenum disulfide, where the effects of satellites on PES, XAS and resonant AES are analyzed to varying degrees, and to Ag, where resonant AES can give insight into the unoccupied band states, allowing one to distill all dipole-allowed partial densities of states. We then apply theoretical methods to glean insight from core-excitation spectra in lead titanate, lead tungstate and lithium peroxide, illustrating the methods' role in helping identify crystal structures, including as a function of temperature and pressure. Along the way, throughout the talk, our current shortcomings can help suggest the path forward in the future.