Application of the Lennard-Jones (n, m) Potential Function to Quantum Crystals in the Self-Consistent Phonon Theory

The Lennard-Jones (n, m) potential energy parameters for quantum crystals whose structure are b.c.c. and h.c.p. are calculated. The potential parameters are fitted to experimental data of the sublimation energy, zero point volume and zero point compressibility. The obtained results are in turn used to calculate the pressure variations of the dynamical and thermodynamical functions of the crystal lattices of ³He and ⁴He in the reduced second-order self-consistent phonon theory. The results show reasonable agreement with experimental data.