Real-Time Coupled-Cluster Approach for the Cumulant Green’s Function

• Published in: Journal of chemical theory and computation 2020-11, Vol.16 (11), p.6983-6992
• Main Authors: Vila, F. D, Rehr, J. J, Kas, J. J, Kowalski, K, Peng, B
• Format: Article
• Language: English
• Subjects: Clusters; Elementary excitations; Excitation spectra; Green's functions; Nonlinear differential equations; Nonlinear equations; Perturbation theory; Photoelectric emission; Real time; Satellite observation; Spectroscopy and Excited States
• ISSN: 1549-9618; 1549-9626
• DOI: 10.1021/acs.jctc.0c00639

Green’s function methods within many-body perturbation theory provide a general framework for treating electronic correlations in excited states and spectra. Here, we develop the cumulant form of the one-electron Green’s function using a real-time coupled-cluster equation-of-motion approach, in an extension of our previous study (Rehr J.; et al. J. Chem. Phys. 2020, 152, 174113). The approach yields a nonperturbative expression for the cumulant in terms of the solution to a set of coupled first-order, nonlinear differential equations. The method thereby adds nonlinear corrections to traditional cumulant methods, which are linear in the self-energy. The approach is applied to the core-hole Green’s function and is illustrated for a number of small molecular systems. For these systems, we find that the nonlinear contributions yield significant improvements, both for quasiparticle properties such as core-level binding energies and for inelastic losses that correspond to satellites observed in photoemission spectra.