First-Principles Based Model of Spin-state Phase Transition

The nature of spin-state phase transition is investigated with Fe(C₄H₄N₂)\Pt(CN)₄\ that is a novel 3D Hofmann-like compound. The bistability of this system is obtained by the first-principles calculation. It is demonstrated that thermal expansion is the intrinsic force involved in spin-state transition. Based on these results, we suggest a thermal exciting bistable model of spin-state transition with a temperature dependent crystal-field splitting (CFS). Experimental evidence of spin-state phase transition coincides with our theoretical model. This model approaches something fundamental in the mechanism leading to the transition, and it is important in developing new and practical controllable quantum devices.