  A proper treatment of electrostatic interactions is crucial for the accurate
calculation of forces in computer simulations. Electrostatic interactions are
typically modeled using Ewald based methods, which have become one of the
cornerstones upon which many other methods for the numerical computation of
electrostatic interactions are based. However, their use with charge
distributions rather than point charges requires the inclusion of ansatz for
the solutions of the Poisson equation, since there is no exact solution known
for smeared out charges. The interest for incorporating electrostatic
interactions at the scales of length and time that are relevant for the study
the physics of soft condensed matter has increased considerably. Using
mesoscale simulation techniques, such as dissipative particle dynamics (DPD),
allows us to reach longer time scales in numerical simulations, without
abandoning the particulate description of the problem. The main problem with
incorporating electrostatics into DPD simulations is that DPD particles are
soft and those particles with opposite charge can form artificial clusters of
ions. Here we show that one can incorporate the electrostatic interactions
through Ewald sums with point charges in DPD if larger values of coarse
graining degree are used, where DPD is truly mesoscopic. Using point charges
with larger excluded volume interactions the artificial formation of ionic
pairs with point charges can be avoided, and one obtains correct predictions.
We establish ranges of parameters useful for detecting boundaries where
artificial formation of ionic pairs occurs. Lastly, using point charges we
predict the scaling properties of polyelectrolytes in solvents of varying
quality and obtain predictions that are in agreement with calculations that use
other methods, and with recent experimental results.
