TESTING OF PSEUDOPOTENTIALS USED IN CLASSICAL CAR-PARRINELLO SIMULATIONS

Recently a classical scheme of the Car-Parrinello method was proposed to simulate charged colloidal suspensions described by the highly asym metric 'primitive model' of electrolytes. To make the simulations feas ible one has to rely on a pseudopotential picture which smooths out th e counterionic density profile near the macroionic surfaces. Using 'ex act' Monte Carlo simulations of the same model with two macroions only , we critically test the validity of the pseudopotential construction. We find that the effective forces between the macroions and the count erion density fields are satisfactorily described by pseudopotential t heory for strongly interacting macroions. However, for a configuration of nearly touching macroions, there are substantial deviations. Varia nts of linear screening theory lead to less satisfactory comparison wi th the Monte Carlo data than the 'ab initio' calculations supplemented with the pseudopotential picture. Among all linear screening models, the Poisson-Boltzmann-cell model supplemented with a size correction i s found to be the best description.