First‐principles study of electronic structure and ground‐state properties of alkali‐metal sulfides – Li₂S, Na₂S, K₂S and Rb₂S

Abstract

PACS 71.15. Ap, 71.15.Mb, 71.15.Nc, 71.20.Dg, 71.20.Nr First-principles calculations have been performed to investigate the electronic structure and ground-state properties of alkali-metal sulfides Li 2 S, Na 2 S, K 2 S and Rb 2 S using the tight-binding linear muffin-tin orbital (TB-LMTO) method. At ambient conditions these compounds are found to crystallize in the cubic antifluorite (anti-CaF 2 -type) structure. The exchange correlation energy is described in the local density approximation (LDA) using the von-Barth and Hedin parameterization scheme. The calculated groundstate properties of these compounds such as equilibrium lattice parameter and bulk modulus are in agreement with the other theoretical calculations and experiment results. From the results of the electronicstructure calculations, we find that Li 2 S, K 2 S and Rb 2 S are indirect bandgap semiconductors, whereas Na 2 S is found to be a direct bandgap semiconductor.

Structural stability and electronic property in K2S under pressure

“…15 The similar tendency of decrease with atomic mass of X in X 2 S has been also reported on the elastic constants under the same pressure. When the pressure is enhanced, except for the linear decrease of the elastic constant of C 44 , the bulk modulus and the elastic constant of C 11 , C 12 increase in the crystals of Rb 2 S, K 2 S and Na 2 S. Similar trends are also reported in the Li 2 S except for the elastic constants C 44 .…”

FP-LAPW investigation of mechanical and thermodynamic properties of Na2X (X = S and Se) under pressure and temperature effects

“…At low temperatures, the shapes of the curves of C V and C P are similar. As known, the increase of heat capacity with T 3 at low temperatures is due to the harmonic approximation of the [29], c [26], d [20], e [62], f [63], g [64], h [65], i [66], k [67], l [23], m [68], n [69], o [31], p [70]. Debye model.…”

“…In the Na 2 X (X = S, Se) compounds, the metal atoms (Na) are located at (0.25, 0.25, 0.25) and (0.75, 0.75, 0.75) and the atoms (X) are located at (0, 0, 0). These compounds are subjects of many experimental and theoretical works, focusing on structural phase transformation [17][18][19][20][21][22] and electronic properties [23][24][25][26][27]. The electronic band structure of these materials at ambient conditions was discussed [25] using the selfconsistent pseudo-potential method.…”

First Principles Study of Mechanical Stability and Thermodynamic Properties of K2S under Pressure and Temperature Effect

“…A high Pugh B/G ratio is associated with ductility, whereas a low value corresponds to the brittle nature. The critical value which separates ductile and brittle material is 1.75; i.e., if B/G > 1.75, the material behaves in a ductile manner; otherwise the material behaves in a brittle manner [29]. Now we have found that the B/G ratio is 1.54 for this compound, classifying K 2 S as brittle.…”

“…Schon et al [26] implemented the linear combination of atomic orbitals Hartree-Fock (LCAO-HF) method to analyze high pressure structural phase transition of M 2 S compounds. Selfconsistent pseudopotential method, the LCAO-HF and tight-binding linear muffin-tin orbital (TB-LMTO) studies have been reported by Zhuravlev et al [27], Azavant et al [28], and Eithiraj et al [29], respectively, for electronic band structure of alkali metal sulfides. As well, Khachai et al [20] have calculated the elastic properties of the X 2 S (X = Li, Na, K, and Rb) compounds, under pressure effect, using the full potential augmented plane wave plus local orbitals (FP APW+lo) method.…”