Modeling spin-crossover compounds by periodic DFT+U approach

The electronic properties of two spin-crossover compounds, namely, Fe(phen)(2)(NCS)(2) and Fe(btr)(2)(NCS)(2)H2O, are studied with the GGA+U method taking explicitly into account the periodicity of the crystal. The magnetic state of the iron atom (low spin or high spin), which is strongly coupled to the lattice structure, depends on the chosen value for the parameter U and the total energies of various spin states varying linearly on the U parameter, each with a different slope. The adiabatic energy difference between the low and high spin states is in good agreement with the experiment for U=2.5 eV.