Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A simple permutation group approach to spin-free higher-order
  coupled-cluster methods   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.

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The categories of this paper are: stat
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci
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The categories of this paper are: patt-sol