Collective Effects on the Spin-Crossover Energy*

Spin-crossover complexes are potentially important for application in memory devices and molecular switches. Probed experimentally in condensed phases, the underlying physics is a molecular low-high spin energy difference. Computations on a single molecule therefore are common [Chem. Rev. 121, 9927 (2021)]. Calculation of magnetic properties of transition-metal complexes, however, also is known to be sensitive to diverse computational choices that affect description of the spin states, structure, and magnetism [Eur. J. Inorg. Chem. 2014, 4573 (2014)]. From calculations on a set of first-row transition metal complexes using generalized and meta-generalized gradient density functionals [Phys. Rev. Lett. 77, 3865 (1996); J. Phys. Chem. Lett. 11, 8208 (2020)], we discuss the influence of collective effects on energetic differences between results obtained using condensed aggregates and isolated molecules. We find the condensed-phase collective effects can account for differences by as much as 10% of the molecular value, affecting the predictions of spin-crossover transition temperatures.