The interaction between K atoms and the (110)rutile surface was analyzed by performing ab initio Hartree-Fock calculations and molecular dynamics simulations, demonstrating that the interaction is mainly electrostatic. The preferential sites of adsorption were determined, and the effect of the coverage was studied. Our results show a maximum coverage from which it is not possible to model the deposition process by a classical method. This limit corresponds to a K/Ti(surface) ratio of 0.10, which could be related to the maximum decrease of the work function found experimentally.