The accuracy of the approximation depends on the choice of geminal functions w os 12 and w ss 12 . In previous work we have set w ss 12 = κw os 12 , with κ = 0.5 in XCH-BLYP-UW12, or κ = 0 in B-LYP-osUW12, where the same-spin contribution is neglected. In these functionals, the opposite-spin geminal has been a one-parameter exponential function: 36