Particle-hole cumulant approach for inelastic losses in x-ray spectra

作者：Joshua J. Kas, John J. Rehr, J. B. Curtis · 发表于：Physical review. B./Physical review. B · 年份：2016 · DOI：10.1103/physrevb.94.035156 · 被引用次数：41 · 研究领域：X-ray Spectroscopy and Fluorescence Analysis、Electron and X-Ray Spectroscopy Techniques、Advanced Chemical Physics Studies

Inelastic losses in core level x-ray spectra arise from many-body excitations, leading to broadening and damping as well as satellite peaks in x-ray photoemission (XPS) and x-ray absorption (XAS) spectra. Here we present a practical approach for calculating these losses based on a cumulant representation of the particle-hole Green's function, a quasiboson approximation, and a partition of the cumulant into extrinsic, intrinsic, and interference terms. The intrinsic losses are calculated using real-time time-dependent density functional theory while the extrinsic losses are obtained from the $GW$ approximation of the photoelectron self-energy and the interference terms are approximated. These effects are included in the spectra using a convolution with an energy dependent particle-hole spectral function. The approach elucidates the nature of the spectral functions in XPS and XAS and explains the significant cancellation between extrinsic and intrinsic losses. Edge-singularity effects in metals are also accounted for. Illustrative results are presented for the XPS and XAS of both weakly and more correlated systems.