First Principles Simulations of the Infrared Spectrum of Liquid Water Using Hybrid Density Functionals.

We show that first principles hybrid functional (PBE0) simulations of the infrared spectrum of liquid water yields a much better agreement with experimental results than a semilocal functional description; in particular, the quantitative accord with measured stretching and bending bands is very good. Such an improved description stems from two effects: a more accurate account, at the PBE0 level of theory, of the vibrational properties of the monomer and dimer and an underlying structural model for the liquid with a smaller number of hydrogen bonds and oxygen coordination than those obtained with semilocal functionals. The average electronic gap of the liquid is increased by 60% with respect to the PBE value, when computed at the PBE0 level of theory, and is in fair agreement with experimental results.