Accurate State Energetics in Spin-Crossover Systems using Pure Density Functional Theory

Abstract

The energy difference between different spin states of systems with transition metals is an outstanding challenge for electronic structure calculation methods. The small energy difference between high- and low-spin states in spin-crossover systems makes most post-Hartree-Fock or Density Functional Theory-based methods provide inaccurate values. A test case of twenty systems showing spin transitions has been used to evaluate the accuracy of a new family of meta-GGA (Generalized Gradient Approximation) functionals. One of the functionals of this new family provides comparable or even better values to the best functional reported so far for this type of systems, the TPSSh hybrid meta-GGA functional, but without having to use the exact exchange term. It also improves the results obtained with the r²SCAN meta-GGA functional, which was the best alternative to the TPSSh hybrid functional. This makes it possible to calculate the spin energetics of any kind of compounds, especially large systems or those involving periodic structures where the exact exchange requires large computational resources.