Cooperativity of Spin Crossover Complexes: Combining Periodic Density Functional Calculations and Monte Carlo Simulation.
The total enthalpies of the 16 different spin conﬁgurations that can be realized in the unit cell of the archetype spin crossover complex [Fe(phen)2(NCS)2] (phen = 1,2-phenanthroline) were calculated, applying periodic density functional theory combined with the Hubbard model and the Grimme-D2 dispersion correction (DFT+U+D2). The obtained enthalpy differences between the individual spin conﬁgurations were used to determine spin couplings of an Ising-like model, and subsequent Monte Carlo simulations for this model allowed the estimation of the phenomenological interaction parameter Γ of the Slichter-Drickamer model, which is commonly used to describe the cooperativity of the spin transition. The calculation procedure described here-which led to an estimate of about 3 kJ·mol-1 for Γ, in good agreement with experiment-may be used to predict from ﬁrst principles how modiﬁcations of spin crossover complexes can change the character of the spin transition from gradual to abrupt and vice versa.
['Kreutzburg|Lars|L|', 'Hübner|Christian G|CG|', 'Paulsen|Hauke|H|']
spin crossover density functional calculations Monte Carlo simulation Hubbard model Ising model Slichter–Drickamer model solid state