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

C. Dahnken·M. Aichhorn·W. Hanke·E. Arrigoni·M. Potthoff
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Abstract

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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C. Dahnken, M. Aichhorn, W. Hanke, E. Arrigoni, M. Potthoff. 2004-09-01. Variational cluster approach to spontaneous symmetry breaking: The itinerant antiferromagnet in two dimensions. https://doi.org/10.1103/physrevb.70.245110

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