The often pleasant experience of driving an automobile is dependent upon the optimum performance of a wide range of chemical and physical systems. The design and manufacture of these systems can be aided by the application of quantum mechanics to improve our understanding of their performance at the atomistic level. Surfaces in particular can be exceedingly complex and therefore not easily analyzed using experimental methods, particularly in industrial applications such as the automobile. In this presentation we highlight work in two areas that illustrates how density-functional theory calculations can be used to provide a framework of understanding to enable predictions regarding properties and structures of complex surface layers in a realistic environment. In the first application, a-M₂O₃ (0001) surfaces with M= Al, Fe, and Cr are allowed to exchange atoms with multiple species in the environment across a range of temperatures, pressures, and concentrations. This exchange has a dramatic effect on the relative Gibbs free energies of the possible (1 x 1) surfaces, and is necessary to obtain theoretical predictions consistent with experimental results. In the second application, it is shown how the structure and bonding of iron mono- and disulfides in thin boundary layer films can be related to the surface energy and tribological performance in gear systems.