The theoretical investigation of polar crystal surfaces in solution involves methodological issues that have not been entirely resolved. Here we present results of molecular dynamics simulations of potash alum surfaces in contact with aqueous solution. As a prerequisite for this study, we developed a classical, empirical model potential for this complex inorganic material. The resulting rigid ion force field was carefully tested, and we could show its ability to reproduce a wide range of experimental results. Using this force field, we studied the (111) surface of potash alum and compared various ways of simulating this polar surface. By establishing the stability of a charged, in addition to the reconstructed crystal surface usually assumed, we question the common practice of excluding the existence of such charged surface terminations a priori.