Chemical Physics Seminar
X-ray spectroscopy provides a detailed, but indirect method for studying materials properties such as coordination, bonding, and local electronic structure. Increasingly, sophisticated computational approaches are used to connect measured spectra to these underlying properties. The Bethe-Salpeter equation (BSE) approach has been shown to provide excellent predictions of both x-ray absorption and resonant emission spectra, provided that the structure of a material is known. This success gives us confidence to move beyond reproducing spectra of known structures. The BSE approach can also be used to pinpoint the physical origins of spectral features, predict unknown structures from comparisons to their measured spectra, and highlight discrepancies indicative of limitations in the modeling of the ground-state system.
In this talk I will introduce the OCEAN code and the main ideas behind the BSE. I will discuss battery-related examples where OCEAN calculations are used to identify dopant sites in spinel lithium titanate and resonant emission fingerprints of oxygen oxidation. Afterwards I will explore divergences between calculated and measured spectra of simple nitrate salts. These divergences emphasize the roles of vibrational disorder and many-body lifetime broadening in modifying spectral shapes. I will discuss how these two effects can be incorporated into our BSE method.