(222ax) Isolating the Non-Polar Contributions to the Intermolecular Potential for Water

An accurate water intermolecular potential model is required to predict the structure and properties of water. Water is generally modeled as a non-polarizable rigid molecule with an effective pair potential consisting of a center-to-center Lennard-Jones (LJ) potential and coulombic interactions between charges representing hydrogen and oxygen sites. Due to the large number of parameters, a unique solution for the parameters cannot be obtained for even this simplified model of water. Several potential models have been developed depending on the data used to fit the parameters. Here we show that with the Lorentz-Berthelot rule, the SPC/E[1] model under predicts the solubility of water in alkanes by an order of magnitude compared with experimental data. Since the solubility of water in alkanes is very small, there are negligible water-water interactions and water interacts only with the alkanes through non-polar LJ interactions. This is a good test for the LJ parameters of the water model. We find that a much higher value of energy (1.829KJ/mol) for water is required to match the experimental solubility. Since in this limit charges do not affect the properties, LJ parameters obtained here are independent of the charges.

References

1.            Berendsen, H., J. Grigera, and T. Straatsma, The missing term in effective pair potentials. Journal of Physical Chemistry, 1987. 91(24): p. 6269-6271.