We present results of ab initio total energy calcns. and mol.-dynamics simulations of dye mols. on the NaCl(100) surface. The investigations conc. on the flat dye mols. 3,3'-dimethyloxacarbocyanine, [C19H17N2O2]+, which form sandwich-like structures if closely packed, and the cyanine mol. bis(1,3,3-trimethyl-2-indolinyl)monomethinium, [C21H23N2]+, which shows a typical stereochem. deformation due to two repulsive Me groups. The mol.-dynamics simulations are able to reproduce the exptl. obsd. configurations of the charged dye mols. on surfaces.