5 research outputs found
Harmonic surface mapping algorithm for electrostatic potentials in an atomistic/continuum hybrid model for electrolyte solutions
Simulating charged many-body systems has been a computational demanding task
due to the long-range nature of electrostatic interaction. For the multi-scale
model of electrolytes which combines the strengths of atomistic/continuum
electrolyte representations, a harmonic surface mapping algorithm is developed
for fast and accurate evaluation of the electrostatic reaction potentials. Our
method reformulates the reaction potential into a sum of image charges for the
near-field, and a charge density on an auxiliary spherical surface for the
far-field, which can be further discretized into point charges. Fast multipole
method is used to accelerate the pairwise Coulomb summation. The accuracy and
efficiency of our algorithm, as well as the choice of relevant numerical
parameters are demonstrated in detail. As a concrete example, for charges close
to the dielectric interface, our method can improve the accuracy by two orders
of magnitudes compared to the Kirkwood series expansion method.Comment: 17 pages, 5 figure
Effects of image charges, interfacial charge discreteness, and surface roughness on the zeta potential of spherical electric double layers
We investigate the effects of image charges, interfacial charge discreteness,
and surface roughness on spherical electric double layers in electrolyte
solutions with divalent counter-ions in the setting of the primitive model. By
using Monte Carlo simulations and the image charge method, the zeta potential
profile and the integrated charge distribution function are computed for
varying surface charge strengths and salt concentrations. Systematic
comparisons were carried out between three distinct models for interfacial
charges: 1) SURF1 with uniform surface charges, 2) SURF2 with discrete point
charges on the interface, and 3) SURF3 with discrete interfacial charges and
finite excluded volume. By comparing the integrated charge distribution
function (ICDF) and potential profile, we argue that the potential at the
distance of one ion diameter from the macroion surface is a suitable location
to define the zeta potential. In SURF2 model, we find that image charge effects
strongly enhance charge inversion for monovalent interfacial charges, and
strongly suppress charge inversion for multivalent interfacial charges. For
SURF3, the image charge effect becomes much smaller. Finally, with image
charges in action, we find that excluded volumes (in SURF3) suppress charge
inversion for monovalent interfacial charges and enhance charge inversion for
multivalent interfacial charges. Overall, our results demonstrate that all
these aspects, i.e., image charges, interfacial charge discreteness, their
excluding volumes have significant impacts on the zeta potential, and thus the
structure of electric double layers.Comment: 11 pages, 10 figures, some errors are change