Molecular dynamics of spin crossover: The (P,T) phase diagram of [Fe(PM-BIA)₂(NCS)₂]

The spin crossover properties and the domains of existence of the different phases for the [Fe(PM-BIA)₂(-NCS)₂] complex are obtained from combining DFT and classical molecular dynamics (MD). The potential energy surfaces expressed in the Morse form for Fe-N interactions are deduced from molecular DFT calculations and they allow producing Infra Red and Raman frequencies. These Fe-N potentials inserted in a classical force field lead from MD calculations to the relative energies of the high spin and low spin configurations of the orthorhombic structure. The MD investigations have also allowed assessing the experimental (P, T) phase diagram by showing the monoclinic polymorph in its two spin-states, and generating two triple points.