The accurate modeling of adsorbates on periodic surfaces at low coverages is computationally inefficient with current methodologies, typically requiring large unit cells to minimize unphysical intercell interactions. We propose a novel composite method that effectively cancels the adsorbate鈥揳dsorbate interactions that are otherwise present in such slab calculations. Our method provides a good description of the entire potential energy surface and yields geometrical relaxations at the low coverage limit on periodic surfaces requiring only small unit cells. Simple organic adsorbates have been studied on Si(111) and C(111) surfaces to illustrate the applicability of this new computational approach.