Calculated gas-phase acidities using density functional theory: Is it reliable?

Proton affinities for a diverse set of 35 anions were calculated using 7 different levels of density functional theory (S-null, S-VWN, S-LYP, B-null, B-VWN, B-LYP, and Becke3-PW91). These combinations of functionals cover the range of those that are widely available. The basis-set dependence of these methods was explored using split-valence, double- vs triple-zeta, and correlation- vs noncorrelation-consistent bases (6-31+G(d), and 6-311++G(2df,2pd) vs aug-cc-pVDZ and aug-cc-pVTZ). The results are compared to modest and high-level ab initio acidities (MP2(fc)/6-31 + G(d)/HF/6-31+G(d) and G2, respectively) as well as to experimental results.