2015/05/05 by Alexei Grechnev, A. Grechnev, Grechnev, A. +10
Earth and Planetary Sciences · Engineering · Physics and Astronomy · #FOS: Physical sciences #High-pressure geophysics and materials #Materials Science (cond-mat.mtrl-sci) #Other Condensed Matter (cond-mat.other) #Quantum, superfluid, helium dynamics #Spacecraft and Cryogenic Technologies #cond-mat.mtrl-sci #cond-mat.other
paper · pdf · doi:10.48550/arxiv.1505.00927
Submitted to Phys. Rev. B
openalex publication_date 2015/05/05 · arxiv created 2015/06/18 · arxiv updated 2015/06/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The elastic moduli, elastic anisotropy coefficients, sound velocities and Poisson's ratio of hcp solid helium have been calculated using density functional theory in generalized gradient approximation (up to 30 TPa), and pair+triple semi-empirical potentials (up to 100 GPa). Zero-point vibrations have been treated in the Debye approximation assuming 4He isotope (we exclude the quantum-crystal region at very low pressures from consideration). Both methods give a reasonable agreement with the available experimental data. Our calculations predict significant elastic anisotropy of helium (\triangle P ≈ 1.14, \triangle S1 ≈ 1.7, \triangle S2 ≈ 0.93 at low pressures). Under terapascal pressures helium becomes more elastically isotropic. At the metallization point there is a sharp feature in the elastic modulus CS, which is the stiffness with respect to the isochoric change of the c/a ratio. This is connected with the previously obtained sharp minimum of the c/a ratio at the metallization point. Our calculations confirm the previously measured decrease of the Poisson's ratio with increasing pressure. This is not a quantum effect, as the same sign of the pressure effect was obtained when we disregarded zero-point vibrations. At TPa pressures Poisson's ratio reaches the value of 0.31 at the theoretical metallization point (Vmol=0.228 cm3/mol, p=17.48 TPa) and 0.29 at 30 TPa. For p=0 we predict a Poisson's ratio of 0.38 which is in excellent agreement with the low-p-low-T experimental data.