CRITICAL-DYNAMICS OF A DYNAMICAL VERSION OF THE CLASSICAL HEISENBERG-MODEL

We have performed large-scale molecular dynamics simulations of a dyna mical variant of the classical Heisenberg model in which the spins are replaced by interacting ''linear molecules,'' each of which has two r otational degrees of freedom. The Hamiltonian consists of rotational k inetic-energy terms as well as nearest-neighbor Heisenberg-like intera ctions -JS(i) . s(j), where si is a unit vector specifying the orienta tion of the molecule at lattice site i. Systems of size up to 64(3) sp ins on the simple cubic lattice have been studied, and thermostatting is used to maintain strictly constant temperature. We determined the d ynamic structure function from the time- and space-displaced correlati on functions, and found good agreement with the predictions of the dyn amic scaling theory with a dynamic critical exponent of z = 1.5. Resul ts are compared and contrasted with data from spin-dynamics calculatio ns on classical Heisenberg ferromagnets and antiferromagnets. [S1063-6 51X(96)07605-2]