  We use spin-coherent states as a time-dependent variational ansatz for a
semiclassical description of a large family of Heisenberg models. In addition
to common approaches we also evaluate the square variance of the Hamiltonian in
terms of coherent states. This quantity turns out to have a natural
interpretation with respect to time-dependent solutions of the equations of
motion and allows for an estimate of quantum fluctuations in a semiclassical
regime. The general results are applied to solitons, instantons and vortices in
several one- and two-dimensional models.
