Real-time EOM-CCS Green's function method for the core spectral functions*

X-ray photoemission spectra (XPS) typically exhibit satellite peaks associated with many-body excitations that have proved difficult to simulate from first principles. We address this problem using a real-time equation-of-motion coupled-cluster-singles (RT-EOM-CCS) approach for the core spectral function. RT methods provide a versatile approach to electronic response, but have not been widely applied using CC theory. In RT-EOM-CCS, the Green's function (GF) for an N-electron system is computed from the overlap between the initial core-excited |N-1> wavefunction and its time-propagated form |N-1,t>. The latter is approximated using a CC ansatz with time-dependent amplitudes. The EOM of the overlap is solved using a centered predictor-corrector approach. We show that the form of the overlap is analogous to that in the static CC equations, and that the form of the GF is related to that in the cumulant approach.¹ Finally, we present results for low N systems.
1. J. J. Rehr, F. D. Vila, K. Kowalski and B. Peng, APS March Meeting, 2020.