On the Debye temperature and Grüneisen parameters for hexagonal close-packed crystals consisting of p-H2 and o-D2 molecules

The expressions for the Debye temperature Θ as well as for the first (γ = −[∂ln(Θ)/∂ln(V)]T) and second (q = [∂ln(γ)/∂ln(V)]T) Grüneisen parameters are derived based on the Mie-Lennard-Jones pair atomic interaction potential. The conditions imposed on the Θ(V/V0), γ(V/V0), and q(V/V0) dependences for V/V0 → 0 and for V/V0 → ∞ are analyzed. Here, V/V0 is the ratio of the molar volumes for pressure P at temperature T and for P = 0 at T = 0 K. Calculations are performed for crystals of parahydrogen and orthodeuterium at T = 0 K for V/V0 ranging from 1.30 to 0.01. Good agreement is reached between the calculated dependences and experimental data. The behavior of dependences Θ(V/V0), γ(V/V0), and q(V/V0) upon a variation of the isotopic composition of the crystal is analyzed.