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

Area of Science:

• Materials Science
• Computational Chemistry
• Solid State Physics

Background:

• Spin crossover (SCO) complexes exhibit bistability between distinct spin states.
• Understanding SCO cooperativity is crucial for designing materials with tunable properties.
• The [Fe(phen)2(NCS)2] complex serves as a model system for studying spin transitions.

Purpose of the Study:

• To calculate total enthalpies for various spin configurations in [Fe(phen)2(NCS)2].
• To determine spin couplings and estimate the phenomenological interaction parameter (Γ) of the Slichter-Drickamer model.
• To establish a first-principles method for predicting SCO cooperativity and transition abruptness.

Main Methods:

• Periodic density functional theory (DFT) with Hubbard U (DFT+U) and Grimme-D2 dispersion correction.
• Ising-like model for spin couplings derived from calculated enthalpy differences.
• Monte Carlo simulations to estimate the Slichter-Drickamer interaction parameter (Γ).

Main Results:

• Calculated enthalpies for 16 distinct spin configurations of [Fe(phen)2(NCS)2].
• Estimated the phenomenological interaction parameter Γ to be approximately 3 kJ·mol−1.
• Demonstrated good agreement between calculated Γ and experimental values.

Conclusions:

• The developed computational procedure accurately predicts SCO cooperativity.
• This first-principles approach can guide the design of SCO materials with tailored transition characteristics.
• Modifications to SCO complexes can be rationally predicted to shift transitions from gradual to abrupt or vice versa.