The Critical Temperature of Quantum Spin Model Determined with Variational-Cumulant Expansion |
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Authors: | CHEN Tianlun WANG Qing LIU Ruijie |
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Institution: | 1. Department of Physics, Nankai University, Tianjin 300071, China;
2. Department of Physics and Astronomy, State University of New York at Buffalo, Buffalo, NY 14260, USA |
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Abstract: | The variational-cumulant expansion (VCE)methodis used to calculate the quantum XY model, for which the trial action S0 does not commute with the action S, with arbitrary magnitude of spin on various one-, twe and three-dimensional lattices. The free energy of the model is expanded to the third order and the analytical formulae of critical temperature Tc are given for each order. To testify this method in a wider range, the Heisenberg model on different lattices is also calculated, which has more comparable results. Weighted fitting method of statistical mathematics is adopted to predict Tc of infinite order. |
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