Induction energies for F -(H 2 O) 6 are presented in Fig. E elst + E exch as a function of basis set. For brevity, the "def2" prefix is omitted from the basis set names. Note also that the basis-set selection (and the ordering) is different in (a) as compared to the other panels, in order to highlight the significant errors obtained in the absence of diffuse functions. estimate this value, even with a full complement of diffuse functions; the def2-SVPD value is E ind = -45.2 kcal/mol, which represents 11% error with respect to the def2-QZVPD value. In contrast, the def2-TZVPD value (E ind = -50.0 kcal/mol) represents an underestimate of 0.8 kcal/mol or 2%. To obtain converged results, triple-ζ basis sets with diffuse functions are required and here the hydrogen atom diffuse functions contribute 1.0 kcal/mol, comparing def2-ha-TZVP to def2-TZVPD.