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Coupled Cluster Treatment of the XY model

D. J. J. Farnell·S. E. Krueger·J. B. Parkinson
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Abstract

We study quantum spin systems in the 1D, 2D square and 3D cubic lattices with nearest-neighbour XY exchange. We use the coupled-cluster method (CCM) to calculate the ground-state energy, the T=0 sublattice magnetisation and the excited state energies, all as functions of the anisotropy parameter $γ$. We consider $S=1/2$ in detail and give some results for higher $S$. In 1D these results are compared with the exact $S=1/2$ results and in 2D with Monte-Carlo and series expansions. We obtain critical points close to the expected value $γ=0$ and our extrapolated LSUBn results for the ground-state energy are well converged for all $γ$ except very close to the critical point.

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D. J. J. Farnell, S. E. Krueger, J. B. Parkinson. 1997-06-30. Coupled Cluster Treatment of the XY model. https://doi.org/10.1088/0953-8984%2F9%2F36%2F008

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