STATIC AND DYNAMIC SIMULATION IN THE CLASSICAL 2-DIMENSIONAL ANISOTROPIC HEISENBERG-MODEL - COMMENT

Costa and Costa [Phys. Rev B 54, 994 (1996)] studied vortices in a two -dimensional easy-plane anisotropic ferromagnetic model. They found di fferent vortex behaviors depending on whether the anisotropy parameter lambda is less than or greater than a critical value lambda(c), repro ducing well-known results [Phys. Rev. B 39, 11 840 (1989)]. They claim that the out-of-plane dynamic correlation function S-zz(q,omega) exhi bits a central peak only for lambda>lambda(c), where the static vortic es are of the out-of-plane form, but not for lambda<lambda(c), where t he static vortices are planar. However, their data are physically inac curate for such a conclusion.