The Polarizable continuum potential model in the liquid state Calculations. Density functional computational analysis of the anharmonic vibrational spectrum of liquid water

A Density Functional calculation, using the Gaussian 03 W protocol with the B3LYP functional and the SCRF-Polarizable Continuum model (SCRF-PCM), has been performed on a pentameric unit, constituted by a central water molecule tetrahedrically coordinated to four other surrounding molecules by hydrogen bond (HB) interactions. The calculation has been aimed at reproducing vibrational distributions of the intra-molecular and intermolecular modes, which contribute at widening the stretching and bending O-H bands in the liquid vibrational spectrum, and those at low frequencies, commonly considered intermolecular motions of O-H. ..O stretching and bending type, in the HB tetrahedral network of liquid water. The so called librational large distribution has been also nicely reproduced by this calculation. Energetic and geometrical considerations have been discussed for the equilibrium structure of this pentameric assembly, representing the basic unit presently used to simulate more space-extended structures of liquid water. These are constituted by different domains of ordered (open, or ice-like) and unordered (closed) patches of water clusters. Although the small cluster used in this calculation represents only an approximation to treat the real organization existing in the liquid water complex system, our results seems to reproduce quite well both the vibrational spectrum and the energetic and geometric situations for this very important liquid. (c) 2021 Published by Elsevier B.V.