Pair connectedness functions and percolation
in highly charged electrolyte solutions
F. Bresme and J.L.F. Abascal
ABSTRACT
The structure of highly charged electrolyte solutions is investigated
through a percolation approach.
The systems, simulated by standard Monte Carlo methods, include several 2:2
aqueous solutions with concentrations ranging from 0.25 to 2 M and one 1:1
electrolyte at 1 M concentration.
The ion--ion pair connectedness functions and related quantities have been
computed.
Two ions are considered connected if they are closer than a predefined distance.
Besides this geometric criterion, an energetic condition (i.e., only particles
with unlike charge signs are allowed to form directly connected links) has
also been employed.
The clusters obtained via the geometric and the energetic conditions are
substantially different for the 1:1 electrolyte while the 2:2 solutions
show a cluster structure almost independent on the criterion used.
The percolation thresholds exhibit a non--monotonic variation with
concentration.
A minimum in the percolation threshold has been observed at the higher
concentrations investigated for the 2:2 systems; the shape of the curve
and the limiting values for infinitely dilute solutions suggest the
appearance of a maximum at concentrations lower than those studied in
this paper.
In addition, the critical exponents alpha, gamma and tau have been
computed.
The result for alpha significantly differs from the values reported
for three dimensional lattices but it agrees with those obtained for
the Lennard--Jones fluid.
In contrast, the gamma and tau exponents for 3D lattice systems and for
our electrolyte solutions seem to be coincident.
