Many-Body Contributions to X-Ray Spectroscopy and Relevance to Interfacial Characterization

X-ray spectroscopy is an invaluable tool for the analysis of materials, their surfaces and interfaces. However, studies of functional materials, especially in interfacial contexts, are likely to explore atomic and electronic structure that does not have a pre-existing set of standard spectra, due to the limited, nanoscale dimensions of the interfacial zone or due to the transient nature of its state under operando conditions. Therefore, first-principles simulations can be a vital component in the design of such experiment, either for predicting possible spectral outcomes or interpreting existing measurements. We report on recent advances in the use of a Slater determinant many-electron representation for X-ray transition amplitudes to provide more accurate estimates and more facile interpretation of X-ray absorption, emission and resonant inelastic scattering spectroscopies. The same approach can also provide atom-by-atom interpretation of Electron Energy Loss Spectra (EELS). Applications will be presented in various materials contexts of relevance to energy conversion processes.