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 A_u 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.

已经使用基于密度泛函理论 (DFT) 的第一性原理方法计算了 AuCu ₃型结构中LaX ₃ (X = Sn、Tl、Pb 和 Bi) 化合物的结构、电子、弹性、振动和热力学性质。从计算的LaX ₃电子能带结构可以看出，费米能级附近的能带结构主要由X p轨道和La d轨道组成。随着压力的增加，电导率逐渐降低，电子跃迁变得更加困难。此外，弹性常数 ( C ₁₁ , C ₁₂ , C ₄₄) 和体积模量B、剪切模量G、杨氏模量E 的值随压力增加。此外，泊松比、柯西压力、各向异性指数A _u和体积模量与剪切模量之比B/G 的变化这些化合物的压力表明这四种化合物保持延展性。最后，这是第一次在 0-50 GPa 和 0-600 K 范围内研究热力学性质。使用声子计算，我们发现温度对热力学性质的影响远大于压力影响。特别地，讨论了0 GPa时的声子色散曲线和声子态密度，并报告了压力下Γ点的红外活性声子模式。