Implement VV10 variants of established GGA functionals
A series of reoptimized VV10 correlation functionals have been described by Hujo and Grimme in https://pubs.acs.org/doi/pdf/10.1021/ct200644w
The functionals are as follows
In the original definition, the short-range attenuation parameter b appearing in k and β was fitted to the S22 set30 of NCIs (b = 5.9 for rPW86PBE)
The other parameter C = 0.0093 in EVV10 cNL, which determines the long-range behavior, was always set to its original value (as recommended for GGAs [17]) because initial optimization tests lead to only minor improvements.
We obtain optimum values for b (in atomic units: 4.0 (BLYP), 3.7 (revPBE), 4.8 (B3LYP), 4.5 (B3PW91), and 4.3 (revPBE0), respectively) which are all slightly smaller than that for rPW86PBE.