A NEW FLEXIBLE POLARIZABLE WATER MODEL

Both geometrical flexibility and instantaneously responsive electrical polarization are incorporated into a newly developed 5-site water model that includes one oxygen atom, two partially shielded protons, and two negative charges representing lone pairs. The charges are diffusively distributed. Their values are variable in accordance with the local field. The intramolecular potential function used is the one recently developed by Dang and Pettitt [J. Phys. Chem. 91, 3349 (1987)] for a free water molecule. In order to strengthen the angular dependence of the intermolecular dimer potential, a short-range Morse-type interaction is introduced to represent specific hydrogen bonding interactions. With this model we carry out a classical constant volume molecular dynamics simulation of liquid water at mass density 0.997 g/cm3 and room temperature 298 K. Results for the liquid structure, thermodynamic properties, transport dynamics, dielectric features, and spectroscopic characteristics are presented and compared with the experimental data and other relevant computer simulations. These comparisons show a significant improvement over the 3-site flexible/polarizable model developed earlier at Texas Tech. Though about four times computationally more intensive, the new model is still simple enough to be applied to studies of liquid water in the presence of various types of local perturbations, where electrical fields and orientational effects specifically require geometric flexibility and electrical polarization.