HARD-SPIN MEAN-FIELD THEORY - FORMULATION FOR ISING, XY, AND OTHER MODELS

A new type of mean-field theory, that incorporates the hard-spin conditions of local degrees of freedom, is generally formulated for arbitrary types of local degrees of freedom. The method is implemented by solving its set of coupled equations for the local distribution functions and densities, either analytically and numerically, or by Monte Carlo sampling ("Monte Carlo mean-field theory"). Excellent results are obtained for frustrated Ising models in two and three dimensions. An explicit formulation is given for XY models.