Pressure-dependent structural, mechanical, and electronic properties of XAu (X = Er, Tm) intermetallic compounds from first-principles calculations.

First-principles calculations of the structural parameters, elastic constants, mechanical moduli, Debye temperature, and density of states (DOS) of cubic CsCl-type (B2) XAu (X = Er, Tm) rare-earth intermetallic compounds under hydrostatic compression up to 20 GPa have been performed. The calculations were carried out within the framework of density functional theory (DFT) using the pseudopotential plane-wave (PP-PW) method and the local density approximation (LDA). The calculated elastic constants indicate that both ErAu and TmAu with the CsCl-type (B2) phase satisfy the Born mechanical stability criteria at equilibrium and under pressure up to 20 GPa for ErAu and up to about 19 GPa for TmAu. The zero-pressure structural parameters, elastic constants, and mechanical moduli are generally in good agreement with previously reported theoretical data. The calculated zero-pressure Young's modulus values are 96.61 GPa for ErAu and 73.94 GPa for TmAu, while the corresponding Debye temperatures are 193 K and 167 K, respectively. The obtained results reveal that hydrostatic pressure enhances the stiffness of both compounds, as reflected by the general increase in the elastic constants, acoustic wave velocities, and Debye temperature. Both ErAu and TmAu exhibit ductile behavior according to Pugh's ratio and show noticeable elastic anisotropy. The electronic-structure analysis confirms the metallic character of both compounds, while additional GGA + U calculations indicate that the localized 4f states are sensitive to the Hubbard correction without changing their metallic nature. The pressure-dependent elastic constants and related mechanical and thermodynamic properties of XAu (X = Er, Tm) intermetallic compounds have not been previously reported; therefore, the present results provide useful predictions and reference data for future theoretical and experimental studies.