THE APPLICATION OF THE REACTION-FIELD METHOD TO THE CALCULATION OF DIELECTRIC-CONSTANTS

The behaviour of the popular TIP3P water model has been investigated u sing both molecular dynamics and Monte Carlo simulation procedures. Lo ng-range electrostatic interactions were included through a reaction-f ield treatment, and the nonbonded interactions were either truncated a t the cutoff distance, or smoothly scaled to zero using a switching fu nction. The thermodynamic observables, and in particular the dipole-di pole correlation functions, are found to differ between the two simula tion techniques if a rigid nonbonded cutoff is applied. However, use o f a switching function gives exact agreement between the simulation me thodologies. This difference is ascribed to the effect of energy pumpi ng in the molecular dynamics simulations, and suggests that dielectric constants calculated using this simulation method with the fluctuatio n procedure in conjunction with a reaction field should be reappraised . Thus the Monte Carlo simulation procedure offers a number of intrins ic advantages over molecular dynamics for the calculation of dielectri c constants with a reaction field. The most precise value for the diel ectric constant of TIP3P is calculated to be 102 +/- 3 at 298 K.