Projected coupled cluster theory
- Rice Univ., Houston, TX (United States). Dept. of Chemistry
- Rice Univ., Houston, TX (United States). Dept. of Chemistry and Dept. of Physics and Astronomy
Coupled cluster theory is the method of choice for weakly correlated systems. But in the strongly correlated regime, it faces a symmetry dilemma, where it either completely fails to describe the system or has to artificially break certain symmetries. On the other hand, projected Hartree-Fock theory captures the essential physics of many kinds of strong correlations via symmetry breaking and restoration. Here, we combine and try to retain the merits of these two methods by applying symmetry projection to broken symmetry coupled cluster wave functions. The non-orthogonal nature of states resulting from the application of symmetry projection operators furnishes particle-hole excitations to all orders, thus creating an obstacle for the exact evaluation of overlaps. Here we provide a solution via a disentanglement framework theory that can be approximated rigorously and systematically. Results of projected coupled cluster theory are presented for molecules and the Hubbard model, showing that spin projection significantly improves unrestricted coupled cluster theory while restoring good quantum numbers. The energy of projected coupled cluster theory reduces to the unprojected one in the thermodynamic limit, albeit at a much slower rate than projected Hartree-Fock.
- Research Organization:
- Temple Univ., Philadelphia, PA (United States). Center for the Computational Design of Functional Layered Materials (CCDM); Rice Univ., Houston, TX (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); Welch Foundation
- Grant/Contract Number:
- SC0012575; CHE-1462434
- OSTI ID:
- 1474042
- Alternate ID(s):
- OSTI ID: 1374781
- Journal Information:
- Journal of Chemical Physics, Vol. 147, Issue 6; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
operator theory
Hubbard parameter
full configuration interaction
coupled-cluster methods
many electron systems
zero point energy
correlation-consistent basis sets
self consistent field methods
correlated electrons
statistical thermodynamics