Throughout this optimization, a majority of the parameters remain mostly unchanged, with the difference between the final and initial values less than 0.05 in all but four cases. The c -4 u value changes by 0.0554, while the first through fourth order same-spin B97 coefficients differ more significantly from the initial values than the other components. The greatest change is seen in the c 1 ss coefficient (0.5958). The large change in these values is the reason for the numerous re-optimization cycles performed on the functional. Also of note is the Table : Optimized coefficients for the ωB97X-osUW12-D3(BJ) functional at each stage of the optimization. The first set of coefficients are fitted using energies calculated using the ωB97X functional, subsequent fittings are performed on the training set data obtained using the functional defined in the previous column. The final WM21-D3(BJ) functional parameters are shown in bold. function was made independent of the choice of the functional it was to be used in, the new geminal has been fitted in the presence of the other parts of the functional. In particular the long-range portion is optimized to work with the D3(BJ) dispersion correction, we have previously shown that this term can affect the range of the geminal function. Following the same procedure as for WM21-D3(BJ), we optimize the best standard hybrid functional of the type ωB97X-D3(BJ), looking at figure 2 it can be seen that the best possible hybrid contains 8 linear parameters, with the lowest error functional combination containing the coefficients c sr x , c 0 x = 1c sr x , c 1 x , c 2 x , c 0 ss , c 0 os , c 1 os , c 2 os , and s 8 . This combination has a weighted RMSE on the training and validation sets of 5.49 kcal mol -1 and 3.67 kcal mol -1 respectively. This combination of B97 components is slightly different than the one used in ωB97X-V, which does not include c 2 os , including c 1 ss instead, this combination had weighted training and validation set RMSEs of 5.82 kcal mol -1 and 3.96 kcal mol -1 respectively. We refer to this functional as ωB97X21-D3(BJ).