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An Efficient Implementation of High-Order Coupled-Cluster Techniques Applied to Quantum Magnets |
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| Authors: | Chen Zeng D. J. J. Farnell R. F. Bishop |
| Affiliation: | (1) Department of Physics, University of Manchester Institute of Science and Technology (UMIST), P.O. Box 88, Manchester, M60 1QD, United Kingdom;(2) Department of Physics, Syracuse University, Syracuse, New York, 13210 |
| Abstract: | We illustrate how the systematic inclusion of multi-spin correlations of the quantum spin–lattice systems can be efficiently implemented within the framework of the coupled-cluster method by examining the ground-state properties of both the square-lattice and the frustrated triangular-lattice quantum antiferromagnets. The ground-state energy and the sublattice magnetization are calculated for the square-lattice and triangular-lattice Heisenberg antiferromagnets, and our best estimates give values for the sublattice magnetization which are 62% and 51% of the classical results for the square and triangular lattices, respectively. We furthermore make a conjecture as to why previous series expansion calculations have not indicated Néel-like long-range order for the triangular-lattice Heisenberg antiferromagnet. We investigate the critical behavior of the anisotropic systems by obtaining approximate values for the positions of phase transition points. |
| Keywords: | Coupled-cluster method quantum magnets strongly correlated spin lattices high-order LSUBm approximations generalized Né el model state square-lattice XXZ model triangular-lattice Heisenberg antiferromagnet ket-state parametrization bra-state parametrization lattice animals and fundamental configurations ground-state energy sublattice magnetization critical points quantum order quantum phase transitions |
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