Development in the DFT Estimates of Magnetic Couplings in Chromium-Based Molecular Rings from an Optimally-Tuned Range separated Hybrid Functional

The Cr₈ molecule, as well as its homo- and hetero-metallic derivatives, belongs to a class of molecular nanomagnets which are extensively studied for a number of fundamental aspects and envisaged applications. However, estimating accurately their magnetic couplings from first principles calculations has proven to be difficult. Here we present progress in this area for two prototypical molecular rings, Cr₈ and Cr₇Ni^-, using density functional theory with an optimally-tuned range separated hybrid (OT-RSH) functional. This approach has been shown to allow for an accurate description of the electronic structure in a variety of more simple molecular systems. Here, we show that it is also capable of producing highly accurate magnetic exchange parameters for both molecules despite their complexity, while improving the overall description of the electronic structure, especially with respect to the energy of the frontier orbitals. For the Cr₇Ni^- ring, the values of the magnetic couplings found are distinguished by a unique site distribution and lead to excellent agreement with experiment.