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Rotational g Tensors Calculated Using Hybrid Exchange-Correlation Functionals with the Optimized Effective Potential Approach

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journal contribution
posted on 09.05.2006 by Andrew M. Teale, Trygve Helgaker, David J. Tozer
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.