@article{cong_wang_simple_2018,
	title = {A simple permutation group approach to spin-free higher-order coupled-cluster methods},
	url = {https://arxiv.org/pdf/1805.00565.pdf},
	abstract = {We present a general-order spin-free formulation of the single-reference closed-shell coupled-cluster method. We show that the working equations of a fully biorthogonal contravariant projection formulation of the residual equations, as near-universally used in closed-shell CCSD, can also be defined at the CCSDT and CCSDTQ levels, despite singularities in the spin projection manifolds. We describe permutation-group based techniques for obtaining and simplifying the equations encountered in general second-quantization-based methods; this includes a permutation group based approach of evaluating second-quantized matrix elements into tensor contraction networks, and the use of Portugal's double coset canonical representation technique [Int. J. Mod. Phys. C 13, 859 (2002)] for eliminating redundant terms. A computer implementation of our techniques is simple, because no operator-valued symbolic algebra is required. Explicit working equation lists for closed-shell CCSD, CCSDT, and CCSDTQ in the semi-biorthogonal formulation are provided. We also release open-source computer programs for both deriving and numerically evaluating these equations.},
	author = {{Cong Wang} and {Gerald Knizia}},
	month = may,
	year = {2018},
	keywords = {quantum chemistry, uses sympy},
}

{"_id":"C5FkRAY22cJzFBdpr","bibbaseid":"congwang-geraldknizia-asimplepermutationgroupapproachtospinfreehigherordercoupledclustermethods-2018","authorIDs":[],"author_short":["Cong Wang","Gerald Knizia"],"bibdata":{"bibtype":"article","type":"article","title":"A simple permutation group approach to spin-free higher-order coupled-cluster methods","url":"https://arxiv.org/pdf/1805.00565.pdf","abstract":"We present a general-order spin-free formulation of the single-reference closed-shell coupled-cluster method. We show that the working equations of a fully biorthogonal contravariant projection formulation of the residual equations, as near-universally used in closed-shell CCSD, can also be defined at the CCSDT and CCSDTQ levels, despite singularities in the spin projection manifolds. We describe permutation-group based techniques for obtaining and simplifying the equations encountered in general second-quantization-based methods; this includes a permutation group based approach of evaluating second-quantized matrix elements into tensor contraction networks, and the use of Portugal's double coset canonical representation technique [Int. J. Mod. Phys. C 13, 859 (2002)] for eliminating redundant terms. A computer implementation of our techniques is simple, because no operator-valued symbolic algebra is required. Explicit working equation lists for closed-shell CCSD, CCSDT, and CCSDTQ in the semi-biorthogonal formulation are provided. We also release open-source computer programs for both deriving and numerically evaluating these equations.","author":[{"firstnames":[],"propositions":[],"lastnames":["Cong Wang"],"suffixes":[]},{"firstnames":[],"propositions":[],"lastnames":["Gerald Knizia"],"suffixes":[]}],"month":"May","year":"2018","keywords":"quantum chemistry, uses sympy","bibtex":"@article{cong_wang_simple_2018,\n\ttitle = {A simple permutation group approach to spin-free higher-order coupled-cluster methods},\n\turl = {https://arxiv.org/pdf/1805.00565.pdf},\n\tabstract = {We present a general-order spin-free formulation of the single-reference closed-shell coupled-cluster method. We show that the working equations of a fully biorthogonal contravariant projection formulation of the residual equations, as near-universally used in closed-shell CCSD, can also be defined at the CCSDT and CCSDTQ levels, despite singularities in the spin projection manifolds. We describe permutation-group based techniques for obtaining and simplifying the equations encountered in general second-quantization-based methods; this includes a permutation group based approach of evaluating second-quantized matrix elements into tensor contraction networks, and the use of Portugal's double coset canonical representation technique [Int. J. Mod. Phys. C 13, 859 (2002)] for eliminating redundant terms. A computer implementation of our techniques is simple, because no operator-valued symbolic algebra is required. Explicit working equation lists for closed-shell CCSD, CCSDT, and CCSDTQ in the semi-biorthogonal formulation are provided. We also release open-source computer programs for both deriving and numerically evaluating these equations.},\n\tauthor = {{Cong Wang} and {Gerald Knizia}},\n\tmonth = may,\n\tyear = {2018},\n\tkeywords = {quantum chemistry, uses sympy},\n}\n\n","author_short":["Cong Wang","Gerald Knizia"],"key":"cong_wang_simple_2018","id":"cong_wang_simple_2018","bibbaseid":"congwang-geraldknizia-asimplepermutationgroupapproachtospinfreehigherordercoupledclustermethods-2018","role":"author","urls":{"Paper":"https://arxiv.org/pdf/1805.00565.pdf"},"keyword":["quantum chemistry","uses sympy"],"metadata":{"authorlinks":{}},"html":""},"bibtype":"article","biburl":"https://bibbase.org/zotero-group/nicoguaro/525293","creationDate":"2020-07-15T19:11:20.567Z","downloads":0,"keywords":["quantum chemistry","uses sympy"],"search_terms":["simple","permutation","group","approach","spin","free","higher","order","coupled","cluster","methods","cong wang","gerald knizia"],"title":"A simple permutation group approach to spin-free higher-order coupled-cluster methods","year":2018,"dataSources":["YtBDXPDiQEyhyEDZC"]}