First-principles study of structural, electronic, elastic, vibrational and thermodynamics properties of LaX3 (X=Sn, Tl, Pb and Bi) compounds under pressure

Abstract

The structural, electronic, elastic, vibrational and thermodynamics properties of the LaX3 (X = Sn, Tl, Pb and Bi) compounds in AuCu3 type structure have been calculated using first-principles method based on the density functional theory (DFT). From the calculated electronic band structure of LaX3, we can see that the energy band structure near the Fermi level is mainly composed of X p orbitals and La d orbitals. With the enhancing pressure, the electrical conductivity decrease gradually and the electron transition becomes more difficult. Moreover, the elastic constants (C11, C12, C44) and the values of bulk modulus B, shear modulus G, Young's modulus E increase with pressure. In addition, the change of Poisson's ratio, Cauchy pressure, anisotropy index Au and the ratio of bulk modulus to shear modulus B/G of these compounds with pressure show that the four compounds remain ductile. Finally, it is the first time that the thermodynamics properties were investigated in the range of 0–50 GPa and 0–600 K. Using the phonon calculations, we found that the temperature effect on the thermodynamics properties is much greater than the pressure effect. Particularly, the phonon dispersion curves and phonon density of states at 0 GPa are discussed and the infrared active phonon modes at Γ point under pressure are reported.