How to build a better pair potential for water

With the objective of improving the effective pair potentials for water, we develop a potential model that employs diffuse charges, in addition to the usual point charges, on the oxygen and hydrogen atoms, to account for charge penetration effects. The potential has better transferability from the liquid to gaseous phases since, unlike many existing models, it does not require an enhanced dipole moment. As a result it accurately reproduces the structural and thermodynamic properties of water over a wide range of conditions. Moreover, by allowing for electronic polarization when evaluating the total dipole moment of the simulated fluid, the model leads to the correct value of the dielectric constant for virtually any state point. At room temperature the calculation produces an average dipole moment of 3.09 D, in accord with recent theoretical and experimental evaluations. This supports the idea that induction effects in water are more important than previously expected. (C) 2001 American Institute of Physics.