INTERATOMIC POTENTIALS CALCULATED FROM EQUATIONS OF STATE - LIMITATION OF FINITE STRAIN TO MODERATE-K

Conditions under which equations of state (EOS) are valid are investigated by calculating implicit interatomic potentials for fixed structures. Third-order Eularian finite strain yields physically realistic potentials only for approximately 3.8 < K'o < B. The upper limit B depends on the size of the long range attractive potential relative to that of the repulsive potential, and is approximately 6 for neutral solids or incompressible materials (e.g., argon or MgO), or approximately 8 for ionic or soft solids (e.g., NaCl). Thus, 3rd order yields reasonable interatomic potentials for the range K'o commonly occupies. Potentials for 4th order are unrealistic if K''o varies by more than a few % from the 3rd order value. Vinet, Ferrante, Rose and Smith's EOS should be used instead for materials with high K'o (e.g., gases or liquids) because it yields valid potentials for all values of the elastic parameters.