Periodic Density Functional Calculations in Order to Assess the Cooperativity of the Spin Transition in Fe(phen)2(NCS)2

Periodic density functional calculations combined with the Hubbard model (DFT+U) have been performed for the archetype spin crossover complex Fe(phen) 2 (NCS) 2 with phen = 1,2-phenanthroline. The relative energies of the 16 different configurations of two possible spin states for each of the four molecules in the unit cell have been calculated in order to determine from first principles the phenomenological interaction parameter Γ of the Slichter-Drickamer model. These kind of calculations may help to predict important spin crossover characteristics like the abruptness or hysteresis of the transition.