Real-time Equation of Motion Coupled Cluster Green's Function Approach for Satellite Peaks in XPS*

Satellite peaks in x-ray photoemission spectra arise from many body excitations that have heretofore been difficult to simulate from first principles. To address this problem we have developed (F. D. Vila et al., J. Chem. Theory Comput. doi:10.1021/acs.jctc.0c00639) a real-time equation-of-motion coupled-cluster (RT-EOM-CC) method for the core spectral function where the Green's function is computed from the overlap <N-1|N-1,t> between the initial core-excited wavefunction and its time-propagated form. The time-dependent CC amplitudes are obtained from coupled, first order, nonlinear differential equations using a CC singles ansatz. Here we present a new, efficient extension of the approach to CC doubles implemented in NWChem, where code for each matrix element is generated with the Tensor Contraction Engine. We present results showing that this implementation extends the applicability of RT-EOM-CC to systems with hundreds of electrons. We also discuss extensions required to include correlations in the ground state.