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A.B. Koudriavtsev, W. Linert:
"Free energy functional of the Ising-like model of spin crossover";
Monatshefte für Chemie, 141 (2010), 601 - 610.

The model of spin crossover based on the Isinglike
Hamiltonian (IHM) has been analysed by deriving the
functional of free energy from the mean-field solutions of
this Hamiltonian. The contribution of the configurational
entropy was found to be identical to that in the functional
of the molecular statistical model (MSM) of spin crossover.
However, the polynomial expansion over composition (xB)
and degree of order (sB) in these functionals differ fundamentally
due to different ways of accounting for the effects
of molecular interactions. It was found that IHM takes into
account next-to-nearest neighbour interactions by introducing
affinities of sublattices towards molecules of given
kinds. This yields a term proportional to the first power of
the degree of order in the functional of IHM, whereas the
MSM free energy is only proportional to sB 2 . The choice of
formal independent variables does not affect the results of
simulations of transition curves provided the functional
remains unaltered. This provides for more flexibility in
numerical simulations of transition curves.

Spin crossover - statistical thermodynamics - molecular interactions - ordering

http://dx.doi.org/10.1007/s00706-010-0315-3