Rotational g tensors calculated using hybrid exchange-correlation functionals with the optimized effective potential approach

The calculation of rotational g tensors using density functional theory (DFT) with hybrid exchange-correlation functionals is considered. A total of 143 rotational g tensor elements in 58 molecules ( 67 isotopic combinations) are calculated using three standard hybrid functionals. Tensor elements determined using an uncoupled approach with orbitals and eigenvalues calculated from the multiplicative optimized effective potential (OEP) constitute a significant improvement over those determined in the conventional coupled manner with a nonmultiplicative exchange-correlation operator. Relative to experimental results, mean absolute errors are reduced by a factor of 2; mean errors and standard deviations are reduced by more than a factor of 3. The results are also an improvement over those determined using a generalized gradient-approximation functional optimized for magnetic response properties. The influence of orbital exchange is investigated for a representative subset of molecules, yielding an optimal amount near 0.3. Rotational g tensors are also determined from coupled-cluster electron densities using a combined DFT/wave-function approach. Being substantially more expensive, they do not offer a notable improvement on the pure DFT values from OEP-based hybrid calculations.