The subtlety of elastic interactions in spin crossover materials

My collaborators and I recently posted a preprintExact mapping from short-ranged harmonic elastic models of spin crossover materials to Ising models with interactions at all length scalesNadeem Natt, Gian Ruzzi, Jace Cruddas, Ross H. McKenzie, Ben J. PowellSpin crossover (SCO) materials are reversible molecular switches found in a wide range of transition metal complexes and metal organic frameworks (MOFs). They exhibit diverse spin state orderings and transitions between them. Here we present an exact mapping from harmonic elastic models to Ising-like models with both a short-range Ising interaction that decays with a power law at large distances and a long-range (infinite-range) Husimi-Temperley interaction that is independent of distance. We apply this mapping to a simple model of SCO frameworks. This provides a microscopic justification for an Ising-Husimi-Temperley model description, which has previously only been justified on phenomenological grounds. Elastic frustration is…