Assessing Local Hybrid Density Functionals for the Prediction of Exchange Coupling Constants in Transition Metal Complexes

The prediction of Spin-Hamiltonian exchange coupling parameters is key for successful modelling of multi-center transition metal complexes (MTMCs) such as single molecule magnets and biocatalyst analogues. Local hybrid functionals, which include a spatially varying proportion of exact exchange, have been proposed as a method for improving the performance of density functional theory (DFT) with these highly magnetic systems. Given DFT is one of the few methods efficient enough for analysis of large MTMCs, it is crucial to understand and improve upon performance and reliability for calculation of coupling parameters and magnetic contributions to energy levels. Here we examine the performance of local hybrid and meta-GGA functionals, including the new r²SCAN functional, for the prediction of coupling parameters in several di-nuclear transition metal complexes. Natural population analysis and qualitative density comparisons rationalize the variation in functional performance and demonstrate the need for further local hybrid functional development.