Ab initio study of thermodynamic properties of bulk zinc-blende CdS: Comparing the LDA and GGA

Abstract

In the present study, we have investigated the phonon and thermodynamic properties of bulk zinc-blende CdS by first-principle calculations within the density functional theory (DFT) and the density functional perturbation theory (DFPT) method using the quasi harmonic approximation (QHA). We calculated the phonon dispersion at several high symmetry directions, density of phonon state, temperature dependence feature of Helmholtz free energy (F), internal energy, bulk modulus, constant-volume specific heat, entropy, coefficient of the volume thermal expansion and Grüneisen parameter estimated with the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation potential and compared them with each other. For internal energy, Helmholtz free energy, constant volume heat capacity and phonon entropy the LDA and GGA results are very similar. But, the LDA gives lattice constants that are smaller than GGA while phonon frequencies, bulk modulus and cohesive energies are larger. On the other hand, the results obtained through the GGA approximation for the coefficient of the volume thermal expansion and Grüneisen parameter are larger than those obtained from LDA.

First-Principles Calculations of Stable Geometric Configuration and Thermodynamic Parameters of Cadmium Sulfide Thin-Film Condensates

“…The sphalerite structure of CdS is stable at low temperatures and has a lattice parameter а=5.825 Å [35]. In this paper the value of the lattice constant is obtained 6.1455 Å, which is relatively higher than the data [4] using the LDA -5.816 Å та GGA -5.990 Å, due to the use of additional atoms for compensation of broken bonds. The wurtzite CdS structure has parameters a = 4.138 Å and c = 6.718 Å [36], and we obtained the value a = 4.543 Å, and c = 6.8758 Å.…”

“…Since thermodynamic parameters of heat capacity, entropy, thermal expansion and Gruneisen parameter for semiconductors are related to other physical propertieselastic and mechanical properties, it is critical to achieve accurate information of thermodynamic properties at certain pressure and temperature for fabrication and application of advanced semiconducting materials [4] The thermodynamic data of the clusters may be useful to estimate the direction of chemical reaction involved during their formation and also helps us to evaluate other thermodynamic functions according to Maxwell's thermodynamic relations [14].…”

“…In the sphalerite structure of CdS, each atom of Cd or chalcogen (S) is located in the center of a regular tetrahedron, in the four vertices of which are the atoms of another element S (Cd), respectively. In this case, the chemical bond between Cd-S atoms is due to the valence electrons Cd-5s 2 and S-3p 4 .…”

“…Therefore, many research groups are focusing on the study of film photovoltaic cells, which are increasingly competing with traditional silicon [2][3]. II-VI semiconductor group has potential applications in solar cell, light-emitting diodes and efficient thin film transistors [4]. Among thin-film systems, heterostructures of the CIS type [5][6], CIGS [7], CdTebased materials [8][9][10] have become the most effective.…”

Electron, phonon, optical and thermodynamic properties of CdTe crystal calculated by DFT

“…Figure 12 shows the constant-volume specific heat capacity for CdTe. As can be seen at high temperature, it almost approaches the Petit-Dulong limit representing that at high temperature, all phonon modes are motivated by the thermal energy according to the observed behaviors of solids at high temperature [42]. At relatively low temperatures, the vibrational excitations arise due to acoustic oscillations.…”