Considering the uniqueness of wetting systems consisting of three components, namely, the surface, liquid and liquid/solid interface, it is desirable to construct interatomic potentials following a consistent policy. To investigate the physical meaning of the behavior in terms of the interatomic potentials, the wetting systems are modeled by simple two-body interatomic potentials derived using ab initio molecular orbital calculations for hypothetical clusters representing the above three components. For In and Sri liquid atoms, spreading occurs on a Cu (111) surface, while in contrast, liquid atoms penetrate the substrate and form a surface alloy in the case of a Pd (111) surface.