Parameterization and evaluation of a flexible water model

The thermodynamic, dielectric, and dynamic properties of a newly parameterized flexible water model are studied using molecular dynamics simulations. The potential function developed is based on the popular simple point charge (SPC) rigid model with the addition of appropriate harmonic and anharmonic energy terms for stretching and bending. Care was taken to account for the self‐polarization and gas‐phase monomer energy corrections during the parameterization, which have typically been ignored in past studies. The results indicate that an increased Lennard‐Jones repulsive coefficient and slightly scaled partial charges are required when adding flexibility to the rigid model potential to reliably reproduce the experimental density, energy, and O ⃛ O radial distribution function of water at 298 K and 1 atm. Analysis of the power spectrum derived from the H‐velocity autocorrelation function allowed the water potential to be evaluated further and refined by adjusting the valence forces to fit the vibrational frequencies of the gas and liquid. Once a consistent set of parameters was determined, the static dielectric properties of the water model were calculated at two temperatures using the reaction field method to treat long‐range forces and correlations. The dielectric constant of 75 ± 7 calculated at 300 K is in good agreement with the experimental value of 78.5. The Kirkwood g factor was also examined for temperature dependence and showed the correct increasing behavior with decreasing T. As a final check of the water potential, the free energies of solvation of a flexible water molecule and neon were predicted using thermodynamic perturbation methods. The calculated solvation energies of −7.0 ± 0.8 for water and 2.7 ± 0.7 for neon are both consistent with the experimental values of −6.3 and 2.7 kcal/mol. Comparisons are made throughout the study with the results of previous rigid and flexible model simulations. © 1995 by John Wiley & Sons, Inc.