Accuracy of computational solvation free energies for neutral and ionic compounds: Dependence on level of theory and solvent model

Gas to aqueous phase standard state (1 atm→1 mol/L; 298.15 K) free energies of solvation (ΔG°solv) were calculated for a range of neutral and ionic inorganic and organic compounds using various levels and combinations of Hartree-Fock and density functional theory (DFT) and composite methods (CBSQ//B3, G4MP2, and G4) with the IEFPCM-UFF, CPCM, and SMD solvation models in Gaussian 09 (G09). For a subset of highly polar and generally polyfunctional neutral organic compounds previously identified as problematic for prior solvation models, we find significantly reduced ΔG°solv errors using the revised solvent models in G09. The use of composite methods for these compounds also substantially reduces their apparent ΔG°solv errors. In contrast, no general level of theory effects between the B3LYP/6-31+G** and G4 methods were observed on a suite of simpler neutral, anionic, and cationic molecules commonly used to benchmark solvation models. Further investigations on monoand polyhalogenated short chain alkanes and alkenes and other possibly difficult functional groups also revealed significant ΔG°solv error reductions by increasing the level of theory from DFT to G4. Future solvent model benchmarking efforts should include high level composite method calculations to allow better discrimination of potential error sources between the levels of theory and the solvation models.