Quantum phase transition in square- and triangular-lattice spin-1/2 antiferromagnets

We use the coupled-cluster method to study ground-state properties of anisotropic S=1/2 antiferromagnets on square and triangular lattices, with the inclusion of arbitrarily long-ranged two-spin correlations. We detect the singularities of various quantities associated with the quantum phase transitions and also compute their critical exponents. The two-spin correlation coefficients for the triangular lattice are found to exhibit an interesting oscillatory behavior in their signs, knowledge of which could assist the implementation of quantum Monte Carlo simulations.