wB97M(2) double hybrid
We'll need to implement the ωB97M(2) double hybrid, as described in https://doi.org/10.1063/1.5025226. Since we already have ωB97M-V, this is quite simple - just putting in the new parameters... However, the complication over the only double hybrid in libxc at the moment, B2PLYP, is that ωB97M(2) is also a range-separated hybrid. (I think there are also several double hybrids that are based on a hybrid functional, too.)