Equation of motion coupled-cluster approach for multi-electron excitations in x-ray spectra

We present a real-time equation of motion coupled cluster approach [1] for calculations of multi-electron excitations in core-level x-ray absorption and emission spectra. Integration of the equations to leading order in particle-hole excitations yields a cumulant representation of the core-hole spectral function. Absorption and emission spectra are then calculated in terms of a convolution of an effective one-body x-ray spectrum and the core-hole spectral function. Comparisons with determinantal approaches and with the Delta-SCF approximation are also discussed. Illustrative calculations are discussed separately [2].
[1] K. Schönhammer and O. Gunnarsson, Phys. Rev. B 18, 6606 (1978).
[2] See F. D. Vila, J. J. Rehr, B. Peng, and K. Kowalski, APS March Meeting 2020.