(69a) Bond Flexibility in Water and the Prediction of Thermo-Physical Properties

There are many alternative intermolecular potentials for water, which reflects the difficulty of accurately predicting all the diverse properties of water. The most commonly used potentials are typically rigid and involve fixed charges. It is well documented that agreement with experiment for a wider range of properties and state points, can be improved by including the effect of polarizability. Polarizable potentials approximate the effect of multibody interactions that arise because the induced dipole of each molecule generates an electric field that affects all other molecules. However, polarizable models are often computationally demanding. In this work, we report molecular simulation calculations for water using an intermolecular potential with flexible bonds. We show that adding bond flexibility mimics the role of polarizability without significantly adding to the computational cost. Results for self-diffusion, shear viscosity and the dielectric constant of water are presented for a wide range of temperatures and pressures and compared with both experimental data and the results of rigid intermolecular potentials. The comparison indicates that introducing bond flexibility can considerably improve the accuracy of predictions for water.