SEMICLASSICAL DESCRIPTION OF HEISENBERG MODELS VIA SPIN-COHERENT STATES

We use spin-coherent states as the basis of a time-dependent variation al ansatz for a semiclassical description of a large family of Heisenb erg models. In addition to following common approaches we also evaluat e the square variance (H-2) - (H)(2) Of the Hamiltonian in terms of co herent states. This quantity turns out to have a natural interpretatio n with respect to time-dependent solutions of the equations of motion and allows an estimate of quantum fluctuations in a semiclassical regi me to be made. The general results are applied to solitons, instantons and vortices in several one-and two-dimensional models.