Nine functions of atomic volume interaction have been established. The values of average atomic volumes and lattice constants of Ag−Cu alloys obtained from each V-function are, respectively, equal to each other and in good agreement with experimental values. But the average atomic volumes of components and the volumes of characteristic atoms obtained from each V-function are different from each other. Only after the correlative study of energy, volume and electronic structure is carried out, can the V-function be correctly chosen, can a knowledge system about the alloys be established, thus providing the base for scientific design of new alloys. The relationships between lattice parameters of metastable phases of Ag−Cu alloys and composition and between average properties and partial molar properties of components are discussed.