AM05 Density Functional Applied to the Water Molecule, Dimer, and Bulk Liquid

We compare results for water obtained with the AM05 exchange-correlation density functional (Armiento, R.; Mattsson, A. E. Phys. Rev. B 2005, 72, 085108) with those obtained with five other pure functionals: LDA, PBE, PBEsol, RPBE, and BLYP. For liquid water, AM05 yields an O-O pair correlation function that is more structured than the ones of PBE and BLYP, which, in turn, are more structured than the one of RPBE. However, LDA and PBEsol yields more structured water than AM05. We show that AM05 yields a H2O dimer binding energy of 4.9 kcal/mol. The result is thus within 0.15 kcal/mol of CCSD(T) level theory (5.02 +/- 0.05 kcal/ mol). We confirm that accuracy in the water dimer binding energy is not a strong indicator for the fidelity of the resulting structure of liquid water.