Ab Initio Calculations of Structural, Lattice Dynamical, and Thermodynamic Properties of Zinc-Blende HgSe and CdSe

The structural, dynamical, and thermodynamic properties of zinc-blende (ZB) mercury selenide (HgSe) and cadmium selenide (CdSe) were systematically explored using an ab initio pseudopotential approach based on the density functional theory (DFT). The optimized lattice constants are in excellent agreement with the available experimental and theoretical results. The electronic properties show semiconducting behavior with a direct bandgap of 0 and 0.36 eV for HgSe and CdSe, respectively. Also, using the linear response approach, the detailed vibration properties of HgSe and CdSe are obtained. According to the calculated phonon dispersion, it is concluded that HgSe and CdSe are dynamically stable in the ground state; several peculiarities in the dispersion curves of these materials are generally similar, but the zone-boundary frequencies and zone-center optical frequencies of HgSe are lower than those of CdSe. The phonon frequencies at the high-symmetry points Gamma, X, and L for HgSe and CdSe are in good agreement with the other theoretical reported. On the other hand, the dielectric properties are investigated and discussed. The results show that the dielectric tensor is diagonal, and the Born effective charge tensor is also isotropic. Finally, based on the lattice dynamical properties, we investigate the thermodynamic properties of both compounds, such as Helmholtz free energy F, internal energy E, entropy S, and specific heat Cv. The results show that HgSe and CdSe exhibit similar but slightly different behaviors in terms of its thermodynamic properties, which is expected because the atoms Hg and Cd are in the same group and exhibit a different atom mass. Most of the results presented in this study are novel and should provide a useful reference for future studies.