The thermodynamic parameters of interaction and the enthalpy parameters are of fundamental importance in the theory of solutions, i.e., the coefficients of the expansion of partial excess thermodynamic functions into series in terms of the concentrations of the dissolved components. In the approximation of pairwise interactions between the impurity atoms in the solution, the above parameters can be computed using the methods of the density functional theory in the electron theory of alloys. As an example, the sub stitutional solid solutions of Au in Ag have been chosen, which are formed by atoms of the components with close chemical properties, in which the deformation interactions should be small, and in which there is no need to take into account the complex magnetic contributions to the pair potentials. The total energy of the dilute solution of Au in Ag and the contributions from the chemical and strain induced interactions to the potentials of pairwise interactions are calculated up to the seventh coordination shell. Quite satisfactory agreement with the thermodynamic parameters obtained from the experimental data has been obtained.