Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Convergence and efficiency of angular momentum projection for many-body
  systems   In many so-called "beyond-mean-field" many-body methods, one creates
symmetry-breaking states and then projects out states with good quantum
number(s); the most important example is angular momentum. Motivated by the
computational intensity of symmetry restoration, we investigate the numerical
convergence of two competing methods for angular momentum projection with
rotations over Euler angles, the textbook-standard projection through
quadrature, and a recently introduced projection through linear algebra. We
find well-defined patterns of convergence with increasing number of mesh points
(for quadrature) and cut-offs (for linear algebra). Because the method of
projection through linear algebra requires inverting matrices generated on a
mesh of Euler angles, we discuss two methods for robustly reducing the number
of required evaluations. Reviewing the literature, we find our inversion
involving rotations about the $z$-axis is equivalent to trapezoidal
"quadrature" commonly used as well as Fomenko projection used for
particle-number projection. The efficiency depends upon the number of angular
momentum $J$ to be projected, but in general inversion methods, including
Fomenko projection/trapezoidal "quadrature" dramatically improve the
efficiency.

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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: cond-mat
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn