title: Coupled-cluster calculations for the ground and excited states of the spin-half XXZ model.
abstract: The coupled-cluster method is applied to the spin-1/2 antiferromagnetic XXZ model on a square lattice by employing an approximation which contains two-body long-range correlations and high-order four-body local correlations. Improvement is found for the ground-state energy, the sublattice magnetization and the critical anisotropy when comparing with the approximation including the two-body correlations alone. We also obtain the full excitation spectrum which is in good agreement with the quantum Monte Carlo results and the high-order spin-wave theory.
authors.affiliation: School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Merdan
authors.forename: Y
authors.initials: Y
authors.lastname: Xian