DFT investigation of elastic, mechanical, vibrational and thermodynamic properties of cadmium dichalcogenides

Ab-initio calculations based on density functional theory (DFT) and ultrasoft pseudopotentials within both generalized gradient approximation (GGA) proposed by Perdew, Burke and Ernzernof (PBE) and local density approximation (LDA) as parametrised by Perdew and Zunger with the electron-ion interaction treated within Rappe Rabe Joannopoulos (rrkjus) pseudopotential, have been performed to investigate the structural, elastic, mechanical, dynamical and thermodynamic properties of Cadmium dichalcogenides (CdS2, CdSe2 and CdTe2) in pyrite structure. The results of the equilibrium lattice constants and bulk moduli are in agreement with experimental and theoretical studies. Their elastic constants were calculated by fitting the computed stress-strain relationship linearly and their respective mechanical properties were then determined from the three independent elastic constants. The vibrational properties were predicted by calculating the phonon dispersion along high symmetry points using density functional perturbation theory (DFPT). The results obtained revealed that these compounds are ductile systems, they exhibit intra-ionic bonding, and are stable mechanically and dynamically in a pyrite structure. The temperature-dependent behaviours of some thermodynamic properties such as the internal energy, vibrational free energy, entropy and constant volume heat capacity for these compounds were also determined.