The interactions of H2O and H2S monomers with Cu(111) in the absence and presence of an external electric field are studied using density functional theory. It is found that the adsorption is accompanied by a rippled pattern of the surface Cu atoms and electron accumulation on the surface Cu atoms surrounding the adsorption site. The response of the H2O/Cu(111) and H2S/Cu(111) interfaces to the external electric field is computed up to the field magnitude of 10(10) V m(-1). The results show that H2O rotates and translates much more with an electric field than H2S does. The extent of the surface deformation changes considerably with the applied electric field, which influences the translation pattern of the adsorbates. On the other hand, the rotation of the adsorbates is correlated to the dipole moment of the molecules and their adsorption energies.