By using an improved nonsymmetric approximation of a self-consistent field for strongly anharmonic crystals and taking account of the anharmony to the sixth order, thermodynamic properties of solid argon were calculated in broad limits of the external parameters. Both the multiparametric pairwise potential of Barker and co-workers, and the 12:6 model potential of Lennard-Jones were used. The three-particle Axelrod-Teller-Muto forces were taken into account. A simple temperature dependence is obtained for the pressure and the isothermal elastic modulus. The results of the computations are compared with experimental data. The best agreement is assured by the Barker-Bobetic potential, while the Barker-Fisher-Watts potential leads to close results. © 1979 Plenum Publishing Corporation.