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Title: Recoupling the singlet- and triplet-pairing channels in single-reference coupled cluster theory

It is well known that single-reference coupled cluster theory truncated to low orders of excitations gives the right answer for the right reason when systems are dominated by dynamical or weak correlation. Static or strong correlation is more problematic, causing often catastrophic breakdown of restricted coupled cluster. This failure can be remedied, e.g., by allowing symmetry breaking in the reference or taking a multi-reference approach, but poses an interesting theoretical problem, especially since many groups have found that simplifying the T 2 operator or the doubles amplitude equations gives better results. In singlet-paired coupled cluster, eliminating the triplet-pairing channel recovers reasonable qualitative behavior for strong correlation at the cost of a decreased description of dynamical correlation in weakly correlated situations. This behavior seems to hold for both closed- and open-shell systems. In this work, we explore the coupling of the singlet- and triplet-pairing channels of T 2 and attempt to recouple them in order to recover dynamical correlation without reintroducing catastrophic failure due to strong correlation. In the weakly correlated regime, these pairing channels are only weakly coupled, and a simple recoupling gives good results. Furthermore, as strong correlation dominates, the coupling strength between the singlet- and triplet-pairing channels increases,more » making it difficult to perturbatively recouple the singlet- and triplet-pairing channels in this regime.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ;  [1]
  1. Rice Univ., Houston, TX (United States)
Publication Date:
Grant/Contract Number:
FG02-04ER15523
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 145; Journal Issue: 13; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Rice Univ., Houston, TX (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS
OSTI Identifier:
1465478
Alternate Identifier(s):
OSTI ID: 1328520

Gomez, John A., Henderson, Thomas M., and Scuseria, Gustavo E.. Recoupling the singlet- and triplet-pairing channels in single-reference coupled cluster theory. United States: N. p., Web. doi:10.1063/1.4963870.
Gomez, John A., Henderson, Thomas M., & Scuseria, Gustavo E.. Recoupling the singlet- and triplet-pairing channels in single-reference coupled cluster theory. United States. doi:10.1063/1.4963870.
Gomez, John A., Henderson, Thomas M., and Scuseria, Gustavo E.. 2016. "Recoupling the singlet- and triplet-pairing channels in single-reference coupled cluster theory". United States. doi:10.1063/1.4963870. https://www.osti.gov/servlets/purl/1465478.
@article{osti_1465478,
title = {Recoupling the singlet- and triplet-pairing channels in single-reference coupled cluster theory},
author = {Gomez, John A. and Henderson, Thomas M. and Scuseria, Gustavo E.},
abstractNote = {It is well known that single-reference coupled cluster theory truncated to low orders of excitations gives the right answer for the right reason when systems are dominated by dynamical or weak correlation. Static or strong correlation is more problematic, causing often catastrophic breakdown of restricted coupled cluster. This failure can be remedied, e.g., by allowing symmetry breaking in the reference or taking a multi-reference approach, but poses an interesting theoretical problem, especially since many groups have found that simplifying the T2 operator or the doubles amplitude equations gives better results. In singlet-paired coupled cluster, eliminating the triplet-pairing channel recovers reasonable qualitative behavior for strong correlation at the cost of a decreased description of dynamical correlation in weakly correlated situations. This behavior seems to hold for both closed- and open-shell systems. In this work, we explore the coupling of the singlet- and triplet-pairing channels of T2 and attempt to recouple them in order to recover dynamical correlation without reintroducing catastrophic failure due to strong correlation. In the weakly correlated regime, these pairing channels are only weakly coupled, and a simple recoupling gives good results. Furthermore, as strong correlation dominates, the coupling strength between the singlet- and triplet-pairing channels increases, making it difficult to perturbatively recouple the singlet- and triplet-pairing channels in this regime.},
doi = {10.1063/1.4963870},
journal = {Journal of Chemical Physics},
number = 13,
volume = 145,
place = {United States},
year = {2016},
month = {10}
}