Building a Benchmark Set of Transition Metal Dimers for Assessing the Prediction of Magnetic Exchange Coupling

Numerous research endeavors have explored the accuracy of density functional approximations (DFAs) when calculating magnetic couplings in transition metal complexes (TMCs). However, the focus has often been on specific TMC groups, and a comprehensive benchmark set is absent. Our objective is to formulate a representative benchmark set for TMCs that balances diversity with manageability. This set will not only assess the efficacy of DFAs in determining magnetic couplings but will also serve as a reference for other methods. The “broken symmetry” technique in DFT is employed to compute the magnetic coupling parameter J for a two-center spin Hamiltonian. J denotes the energy gap between the high spin (HS) and low spin (LS) states of a TMC. Given the complexities of the LS state in DFT, the “broken symmetry” (BS) state is adopted instead. After convergence in both states, Yamaguchi's equation determines J. This benchmark set will help to clarify debates on DFA's comparative effectiveness and guide the development of improved DFAs. Moreover, the benchmark set will stand as a standard for evaluating novel functionals across diverse TMCs.