  Osmotic coefficients, individual and mean activity coefficients of primitive
model electrolyte solutions are computed at different molar concentrations
using the symmetric Poisson-Boltzmann and modified Poisson-Boltzmann theories.
The theoretical results are compared with an extensive series of Monte Carlo
simulation data obtained by Abbas et al. [Fluid Phase Equilib., 2007, 260, 233;
J. Phys. Chem. B, 2009, 113, 5905]. The agreement between modified
Poisson-Boltzmann predictions with the "exact" simulation results is almost
quantitative for monovalent salts, while being semi-quantitative or better for
higher and multivalent salts. The symmetric Poisson-Boltzmann results, on the
other hand, are very good for monovalent systems but tend to deviate at higher
concentrations and/or for multi-valent systems. Some recent experimental values
for activity coefficients of HCl solution (individual and mean activities) and
NaCl solution (mean activity only) have also been compared with the symmetric
and modified Poisson-Boltzmann theories, and with the Monte Carlo simulations.
