An experimental colleague asked me how hard it would be to calculate homolytic bond-dissociation energies for different phosphonates which are involved in a Hydrophosphination. The compounds include aryl and alkyl phosphonates (R2P=O), and the oxygen can be replaced with BH3 (R2P-BH3).
They just want a trend, so the absolute value doesn't matter as long as the model is useful for getting relative trends correct. Blackbox methods like DFT are preferred. Maybe I'm overthinking this but isn't it difficult to calculate BDE because at the dissociation limit the $\sigma$ and $\sigma^*$ become degenerate, and more than one electronic configuration can describe the system (multi-configurational), e.g. $(\sigma)^2$, $(\sigma^*)^2$? Therefore, the correct wavefunction should be sufficiently flexible to treat both configurations on the same footing, which single-references like Hartree-Fock, and DFT cannot. However, multi-configuration techniques like CASPT2/CASSCF are complicated and I'd probably not be able to easily instruct a colleague how to use them easily.
Besides CASPT2/CASSCF, what other methods for calculating homolytic BDEs are good and are fairly "black-box"?