Ab initio study of the structural, electronic, magnetic, mechanical, optical, and dynamical properties of the rare-earth dihydrides MH2 (M= Yb, Sc, Eu, Y, Lu and Gd)

Abstract

Most of the physical properties of rare-earth dihydrides MH2 (M = Yb Sc, Eu, Y, Lu and Gd) have not yet been discovered. The aim of this work is to investigate to the structural, electronic, magnetic, mechanical and optical properties employing density functional theory (DFT) within the VASP code. The computed electronic structures, elastic constants, and lattice parameters of MH2 hydrides are in good agreement with the current experiments and other theoretical studies. The mechanical properties of MH2 (M = Sc, Y, Yb, Eu, Lu and Gd) such as: ductility, elastic moduli, and elastic anisotropy, were evaluated and conferred. The brittle/ductile properties are determined by the bulk/shear ratio B/G and the Cauchy pressure C12–C44. The current work shows that the LuH2, GdH2 and ScH2 hydrides crystallizing in the cubic phase of hydrogen exhibit good mechanical behavior that may be useful for applications in hydrogen storage in the future. In addition, the electronic properties were also investigated in order to present a thorough knowledge of their patterns and verify the metallic behavior trend of these hydrides. The Debye temperature was therefore computed using the single crystal elastic constants and the average sound velocity in accordance with the projected bulk properties of crystalline materials. The optical properties were computed by fitting the dispersion relation of the imagined component. Optical spectra showed a significant absorption coefficient in the in the ultraviolet region of these compounds. The present findings can improve our understanding of rare-earth-based materials towards potential use in the experimental research. Finally, The MH2 (M = Yb Sc, Eu, Y, Lu and Gd) compounds were comprehensively investigated, with a focus on their dynamic characteristics and identification of infrared and Raman active modes. The elastic constant and phonon spectrum calculations revealed the stability of the cubic structure of MH2 under mechanical and dynamic conditions. Furthermore, the study obtained thermal function data, including phonon contributions to internal energy, Helmholtz free energy, entropy, and specific heat at high temperatures.