Cooperativity of Spin Crossover Complexes: Combining Periodic Density Functional Calculations and Monte Carlo Simulation

• Published in: Materials 2017-02, Vol.10 (2), p.172
• Main Authors: Kreutzburg, Lars, Hübner, Christian G, Paulsen, Hauke
• Format: Article
• Language: English
• Subjects: Couplings; Crossovers; Density functional theory; Enthalpy; Interaction parameters; Ising model; Monte Carlo simulation; Parameter estimation; Spin transition; Unit cell
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma10020172

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.