Ising-like hamiltonian and free energy functional: Two fundamentally different models of spin crossover

Abstract

The theoretical models of spin crossover (equilibrium between the high- and low-spin isomers of transition metal complexes) are compared. The models yield similar descriptions of the one-step spin crossover, but different descriptions of the two-step transition curves because of different approaches to the calculation of molecular interactions. The parameters of the Ising-like Hamiltonian reflect the lattice response to the distribution of molecules, and the parameters of the free energy functional reflect the molecular interactions, due to which the sharpness of transition can be correlated with the molecular properties.