Monte Carlo study of the capacitance of the double layer in a model moltensalt

Monte Carlo simulations are reported for charged hard spheres at high densi ty near a charged wall. This system is a simple model for a molten salt dou ble layer. Unfortunately, the reduced temperatures that correspond to exper iment are very small. This results in a large Boltzmann factor. As a result , we are unable to obtain meaningful results for such low values and report results only for moderately low values of the reduced temperature. Even so , our results should be a useful benchmark. Further, we are able to give a qualitative answer to an interesting question. We find that at low temperat ures the capacitance near the point of zero charge increases with increasin g temperature. This agrees with experiment for molten salts and disagrees w ith the behavior of double layer in dissolved salts, which can be modeled w ith low density and high temperature charged hard spheres near a wall. This also disagrees with the predictions of the Gouy-Chapman theory and the mea n spherical approximation. It appears that it is the approximations, and no t the charged hard sphere double layer model, that are at fault for describ ing double layers in molten salts. (C) 1999 American Institute of Physics. [S0021-9606(99)51011-8].