Computer simulations of the dielectric properties of water: Studies of the simple point charge and transferrable intermolecular potential models

Abstract

A series of very long molecular dynamics simulations has been completed for the rigid simple point charge (SPC) and transferrable intermolecular potential 4P (TIP4P) water models with reaction field boundary conditions. The dielectric constant corresponding to these models was evaluated in two ways: (1) by calculating the fluctuations in the mean square dipole moment of the system in the absence of an applied field and (2) by evaluating the polarization response of the system to an applied field. Consistent values for the dielectric constant are obtained by the two methods. For the TIP4P water model, the dielectric constant ε0 is calculated to be ∼50 at 293 K, in agreement with previously published results. For the rigid SPC model, ε0 is calculated to be ∼68 at 300 K and ∼59 at 350 K. The calculated dielectric constant is shown to be very sensitive to the way in which the truncation of long-range forces is treated, although the short-range liquid properties are insensitive to the truncation procedure. The effects on the dielectric response of system size, cutoff radius, and the smoothing of long range interactions at the cutoff boundary are examined. It is found that the introduction of a smoothing function causes perturbations of the water–water angular orientation correlation functions which can result in large errors in the calculated dielectric constant.