We have performed ab initio total energy calcns. and mol. dynamics simulations of dye mols. on NaCl(100) surfaces and in water. The flat trimethine dye mol. [C19H17N2O2]+, which forms sandwich-like structures, and the monomethine cyanine mol. [C21H23N2]+, which shows a typical stereochem. deformation due to two repulsive Me groups, have been simulated. The mol. dynamics simulations are able to reproduce the exptl. obsd. configuration of the charged mols. The behavior of the trimethine [C7H15N2]+ in water has also been simulated.