  We have performed molecular dynamics simulations to study the effect of an
external electric field on a macroion in the solution of multivalent Z:1 salt.
To obtain plausible hydrodynamics of the medium, we explicitly make the
simulation of many neutral particles along with ions. In a weak electric field,
the macroion drifts together with the strongly adsorbed multivalent counterions
along the electric field, in the direction proving inversion of the charge
sign. The reversed mobility of the macroion is insensitive to the external
field, and increases with salt ionic strength. The reversed mobility takes a
maximal value at intermediate counterion valence. The motion of the macroion
complex does not induce any flow of the neutral solvent away from the macroion,
which reveals screening of the hydrodynamic interactions at short distances in
electrolyte solutions. A very large electric field, comparable to the macroion
unscreened field, disrupts charge inversion by stripping the adsorbed
counterions off the macroion.
