Density functional theory investigation on the structural, mechanical, lattice dynamical and thermal properties of nodal-line semimetals CaAgX (X: P, As)

Abstract First-principles calculations based on density functional theory have been used to explore the structural, mechanical, vibrational and thermal properties of Nodal-Line Semimetal CaAgX (X = P, As) for the first time in detail. Firstly, lattice parameters are obtained, and it is found that they are in excellent agreement with previous experimental data. The calculated elastic constants for hexagonal structures satisfy mechanical stability conditions. Thus, using elastic constants, bulk modulus, B/G ratio, shear ratio, Poisson's ratio, Debye temperature and minimum thermal conductivity have been calculated. An attentive investigation of elastic and mechanical properties reveals that these compounds are brittle, and the hardest one is CaAgP, which also has the highest thermal conductivity. Also, the ionic character is dominant in the bonding mechanism for all the studied materials. These materials are also dynamically stable because negative frequencies have not been observed. Lastly, CaAgP reaches the Dulong-Petit limit ( approximately equal to 75 J mol(-1) K) slower than CaAgAs, which agrees with previous experimental study results.