Performance of the coupled cluster and DFT methods for through-space magnetic interactions of nitroxide dimer

We have performed comparisons of several theoretical methods focusing on the through-space interactions of the F2 molecule and nitroxide (dihydronitrosyl) dimer based on the exchange coupling constant. The restricted Hartree–Fock (RHF) based coupled cluster full singles, doubles, and triples (RHF-CCSDT) and approximations to it do not show the exponential decay with increasing intermolecular distance for both antiferromagnetic and ferromagnetic interactions. On the other hand, Mukherjee’s multireference CCSD (MkCCSD) method and the unrestricted HF (UHF) based CCSD (UHF-CCSD) with an approximate spin-projection (AP) method give reliable results. The present benchmark calculations are expected to contribute to the selection of an appropriate density functional theory (DFT) exchange–correlation functionals for larger systems.