TITLE:
First Principles Investigation of the Structure and Properties of Superconducting Cubic Protactinium Hydride PaH3
AUTHORS:
Tao Liu, Tao Gao
KEYWORDS:
α-PaH3 and β-PaH3, Electronic Properties, Mechanical Properties, Thermodynamic Properties, Density Functional Theory (DFT)
JOURNAL NAME:
Journal of Applied Mathematics and Physics,
Vol.11 No.4,
April
28,
2023
ABSTRACT: Cubic protactinium hydrides are very important existing form in superconducting protactinium hydrogen series. In this work, the ground state structure and properties of cubic PaH3 have been studied using the DFT + U method. This systematic study for two bulk properties includes the electronic structures, phonon dispersion curves, structural, mechanical and thermodynamic properties under the effective coulomb U and exchange J PBE + U parameters. Structural relaxation results show that the Pa-H and Pa-Pa distances in α-PaH3 are significantly higher than that in β-PaH3, and the H-H distances in α-PaH3 are slightly smaller than that in β-PaH3. For the ground state electronic structures of α-PaH3 and β-PaH3, we found that α-PaH3 and β-PaH3 are metallic, and the protactinium 5f electronic states and hydrogen have obvious bonding effect, resulting in weakening of the material’s metallicity. This is consistent with observations for the other actinide hydrides such as ThH3 and UH3. The phonon spectrum calculations reveal that the PBE and PBE + U methods give quite different frequencies for the optical branches of phonons of α-PaH3 and β-PaH3. In addition, by including the vibrational entropy and the ZPE using the phonon frequencies obtained from the optimized unit cells we predict that the β-PaH3 phase can not transit into α-PaH3 phase above room temperature.