International Journal of Quantum Chemistry
Spin‐free quantum chemistry. XIV. The infinite interaction range model for ferromagnetism
F. A. Matsen, J.G. Cosgrove, J. Michael Picone
Abstract
Abstract The infinite interaction range model (IIRM) for ferromagnetic systems is presented in its spin‐free formulation. In this formulation the states are labelled by partitions which provide a natural variable for thermodynamic computation. We have extended the calculations of Kittel and Shore by computing to a practical thermodynamic limit (N ∼ 100,000). The heat capacity, magnetic susceptibility and the magnetization of the first two functions exhibit a critical temperature while the magnetization is zero at zero field for all temperatures. Spontaneous magnetization is obtained by linear extrapolation from high field or equivalently by a polarized partition function. Relationships are explored among IIRM, the Heisenberg model and the mean field model. Application to IIRM of the Yang‐Lee condition for a phase transition yields a critical temperature identical to that obtained by the direct calculation.