Coupled Cluster Green's function formulations based on the effective Hamiltonians

Abstract

We demonstrate that the effective Hamiltonians obtained with the downfolding procedure based on double unitary coupled cluster (DUCC) ansatz can be used in the context of Green's function coupled cluster (GFCC) formalism to calculate spectral functions of molecular systems. This combined approach (DUCC-GFCC) provides a significant reduction of numerical effort and good agreement with the corresponding all-orbital GFCC methods in energy windows that are consistent with the choice of active space. These features are demonstrated on the example of four benchmark systems: ${\mathrm{H}}_2\mathrm{O}$, ${\mathrm{N}}_2$, CO, and trans-1,3-butadiene, where DUCC-GFCC calculations were performed for active spaces of various sizes.

GRAPHICAL ABSTRACT

Keywords:

• Coupled cluster
• Green's function
• electronic structure methods

Acknowledgments

This work was supported by the “Embedding Quantum Computing into Many-Body Frameworks for Strongly Correlated Molecular and Materials Systems” project, which is funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, the Division of Chemical Sciences, Geosciences, and Biosciences.  All calculations have been perfromed using the Molecular Science Computing Facility in the Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory (PNNL).   Pacific Northwest National Laboratory is operated by Battelle for DOE under Contract DE-AC05-76RL01830.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the “Embedding Quantum Computing into Many-Body Frameworks for Strongly Correlated Molecular and Materials Systems” project, which is funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, the Division of Chemical Sciences, Geosciences, and Biosciences.