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Variational cluster approach to spontaneous symmetry breaking: The itinerant antiferromagnet in two dimensions

  • Dahnken, C.
  • Aichhorn, M.
  • Hanke, W.
  • Arrigoni, E.
  • Potthoff, M.
Published Article
Publication Date
Sep 01, 2004
Submission Date
Sep 17, 2003
DOI: 10.1103/PhysRevB.70.245110
arXiv ID: cond-mat/0309407
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Based on the self-energy-functional approach proposed recently [M. Potthoff, Eur. Phys. J. B 32, 429 (2003)], we present an extension of the cluster-perturbation theory to systems with spontaneously broken symmetry. Our method applies to models with local interactions and accounts for both short-range correlations and long-range order. Short-range correlations are accurately taken into account via exact diagonalization of finite clusters. Long-range order is described by variational optimization of a ficticious symmetry-breaking field. In comparison with related cluster methods, our approach is more flexible and, for a given cluster size, less demanding numerically, especially at zero temperature. An application of the method to the antiferromagnetic phase of the Hubbard model at half-filling shows good agreement with results from quantum Monte-Carlo calculations. We demonstrate that the variational extension of the cluster-perturbation theory is crucial to reproduce salient features of the single-particle spectrum.

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