Abstract
A stringent test is applied to a set of approximations used, in an earlier work (CCFA) see Frank et al. (ibid., vol.11, p.208 (1978) to calculate Tc for the spin-1/2 Ising ferromagnet. In CCFA, all cumulant averages M2n(2n>or=6) were approximated, for all the cubic lattices, and justified a posteriori. Here, a spin operator reduction relation allows one, for the SC lattice, to approximate only M6, and moreover, to understand the approximation used. The extreme closeness at every stage (within 0.01%) of the present Tc values to those of CCFA gives one confidence method of approximating the M2n for the BCC and FCC lattices as well. Here also, as in CCFA, the M60 value of Tc is within 0.5% of the series approximation value of Sykes et al. (1972).
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