ALTERNATIVE SCHEMES FOR THE INCLUSION OF A REACTION-FIELD CORRECTION INTO MOLECULAR-DYNAMICS SIMULATIONS - INFLUENCE ON THE SIMULATED ENERGETIC, STRUCTURAL, AND DIELECTRIC-PROPERTIES OF LIQUID WATER

Different schemes for treating the electrostatic interactions in molec ular dynamics simulations are investigated: charge-group truncation wi th or without reaction-field correction, atomic truncation with or wit hout reaction-field correction, and Ewald summation. When a reaction-f ield correction is applied, the influence of the size of the radius se lected for the spherical boundary to the continuum is also considered. The different schemes are applied to simple point charge water simula tions, and simulated energetic, transport, structural, and dielectric properties are compared. It is concluded that (i) the inclusion of a r eaction-field correction in a charge-group truncation scheme induces s ignificant changes in different types of properties, and that a number of properties are not identical to those observed using the Ewald sch eme, (ii) when the reaction-field correction is included in an atomic truncation scheme instead, the agreement with the Ewald results is in general improved, and (iii) the increase (decrease) of the radius of t he boundary to the continuum by 0.1 (nm) with respect to the cutoff ra dius induces in both cases a degradation of the simulated properties. Special attention is paid to the calculation of the dielectric permitt ivity from the simulations. Due to the finite size of the statistical ensembles considered, this property is not assumed to be isotropic, an d the degree of anisotropy is used instead as a test for convergence. Since the incorporation of the reaction-field correction into an atomi c truncation scheme leads, when systems of high dielectric permittivit y are considered, to electrostatic interactions which implicitly conta in a (physically reasonable) shifting function and properties which ar e comparable to those obtained using the Ewald method, this scheme is a clear improvement over a charge-group-based truncation when a reacti on-field correction is used in molecular dynamics simulations of nonch arged systems. (C) 1998 American Institute of Physics. [S0021-9606(98) 50315-7].