Spin Crossover Predictions in Transition Metal Complexes using the Density Corrected DFT

The phenomenon of spin-crossover (SCO) in transition metal complexes is of great importance in the development of magnetic materials whose properties are used in visualization, memory, and electrical devices, to mention a few. This phenomenon has been amply studied with Density Functional Theory (DFT) using a broad variety of exchange-correlation (XC) functionals with disappointing outcomes. Such functionals seem incapable of predicting reliably the energy differences between the high- and low-spin configurations. Recently, an approach called HF-DFT, which consists of evaluating the energy of a selected XC functional with the Hartree-Fock (HF) density, has been applied successfully to several problems, including SCO in some iron complexes with small ligands, yielding results that are close to coupled cluster (CC) and Diffusion Monte Carlo calculations, at a much lower computational cost. In this work we show that HF-DFT, using DFT optimized geometries, also offers an excellent alternative to describe SCO in manganocenes with ligands in the cyclopentadienyl rings going from hydrogen to tert-butyl. The results are in excellent agreement with available CCSD calculations.