L. Zhang et al., MOLECULAR-DYNAMICS AND HYPERNETTED-CHAIN EQUATION STUDIES OF SOFT-CORE REPULSIONS IN ELECTROLYTE-SOLUTIONS, Molecular simulation, 12(1), 1994, pp. 1-21
Effects of the repulsive soft core pair potential r(-nu) in 1:1 electr
olytes (1 molar concentration) are studied by molecular dynamics (MD)
simulations and by the hypernetted chain (HNC) integral equations. Com
parisons on the electrolyte structure and dynamical properties are mad
e between a (a) soft ion (SI) model and a (b) soft ion in solution (SI
S) model of electrolyte. In the SI model, there is no solvent, whereas
the SIS model has ions and neutral solvent molecules at liquid densit
y. Inclusion of the solvent imparts liquid-like structure to the ion-i
on pair correlation functions and, if nu not equal infinity, gives ris
e to substantial back scattering oscillations in the velocity autocorr
elation functions with a consequent reduction in the particle self dif
fusion coefficient. Larger values of nu reduce the back scattering;in
the velocity autocorrelation functions. The dynamical behavior of the
ions in the SI model is similar to that of the primitive model electro
lyte (theta = infinity) when nu greater than or equal to 9. In the SIS
fluid, all the pair correlation functions have a similar oscillatory
structure with roughly the same first peak separation for every pair.
Simulation results obtained with the minimum image method compare well
with those obtained with the more expensive Ewald sum method. The HNC
theory predicts pair correlation functions in good agreement with sim
ulations of fluids with continuous repulsive forces but over-predicts
pair correlations in hard sphere fluids.