The spin van der Waals model may be regarded as an infinite-lattice-dimensional limit of the spin-4 anisotropic Heisenberg model. By solution of the generalized Langevin equation, time-dependent behavior is obtained. The geometry of realized Hilbert spaces lends a simple interpretation for critical dynamics.PACS numbers: 05.30.Ch, 05.70.LnCertain statistical mechanical models are exactly solvable at some special limits, providing useful insight into the behavior of these models. For example, when the spin dimensionality in the classical Heisenberg model is made infinitely large, one obtains the spherical model. 1 The static behavior of this model is well understood 2 and has been useful for understanding critical behavior. 1 Consider the spin-^-nearest-neighbor (nn) anisotropic Heisenberg model on a hypercubic lattice of dimensionality Z),

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