Molecular dynamics simulation of the dielectric constant of water: the effect of bond flexibility

The role of bond flexibility on the dielectric constant of water is investigated via molecular dynamics simulations using a flexible intermolecular potential SPC/Fw [Y. Wu, H. L. Tepper, and G. A. Voth, J. Chem. Phys. 128, 024503 (2006)]. Dielectric constants and densities are reported for the liquid phase at temperatures of 298.15 K and 473.15 K and the supercritical phase at 673.15 K for pressures between 0.1 MPa and 200 MPa. Comparison with both experimental data and other rigid bond intermolecular potentials indicates that introducing bond flexibility significantly improves the prediction of both dielectric constants and pressure-temperature-density behavior. In some cases, the predicted densities and dielectric constants almost exactly coincide with experimental data. The results are analyzed in terms of dipole moments, quadrupole moments, and equilibrium bond angles and lengths. It appears that bond flexibility allows the molecular dipole and quadrupole moment to change with the thermodynamic state point, and thereby mimic the change of the intermolecular interactions in response to the local environment.