Structural evolution and electronic properties of CaS: An ab initio study

WOS: 000462471400003CaS crystallizes in cubic NaCl (B1) type structure with symmetry Fm (3) over barm. In this work, the structural and electronic properties of CaS were investigated by considering the Density Functional calculations within the framework of Generalized Gradient Approximation (GGA) under high pressure. The structural change was found at the B1 type structure of CaS. B1 type structure transformed into another cubic CsCl (B2) type structure with symmetry Pm (3) over barm at 36.6 GPa. An intermediate state with symmetry R (3) over barm was predicted during this transition. Besides, the effects of the pressure on the electronic properties of CaS were also studied. Both the B1 and B2 type structures exhibited semiconducting behaviors with direct band gaps at the Gamma-point and R-point, respectively. Intermediate state was searched during this phase change first time in detail. The obtained results were compared with experimental and theoretical ones in the literature

Structural phase transition and electronic properties of CaO under high pressure

WOS: 000445944900002The crystal structure of the CaO compound is studied up to 300 GPa under high hydrostatic pressure using the density functional theory (DFT) with the generalized gradient approximation (GGA). Pressure-volume relationships, structural transitions and electronic properties in CaO compound are investigated using Siesta method. CaO crystallizes in the NaCl-type (B1) structure (space group: Fm (3) over barm) in ambient conditions. CaO transforms from this structure to CsCl-type (B2) structure (space group: Pm (3) over barm) at high pressure. This transformation is based on a intermediate state with space group R (3) over barm. Moreover, the electronic band structures of the B1 and B2 structures of CaO have been calculated. According to this calculation, obtained band gap values are in good agreement with the values reported in the literature

A study of structural phase transitions and optoelectronic properties of perovskite-type hydride MgFeH3: ab initio calculations

WOS: 000467931300001PubMed ID: 31022707In this study, the structural phase transition and optoelectronic properties of perovskite-hydride MgFeH3 under high pressure have been performed by ab initio calculations based on GGA-PBE functional. The phase transitions were observed from the cubic structure (Pm (3) over barm) to the orthorhombic (Pmn2(1)) and (Pmmn) structure. During the phase transition, the R (3) over barm,P1, Pm and P2121(2) intermediate phases were predicted. The energy-volume (E-V) relationships show that the most stable phase is Pm (3) over barm. The lattice parameters and volume increased as based on the phase transforms. From the electronic band analysis, the MgFeH3 shows a metallic character from the cubic to orthorhombic structure. The MgFeH3 indicates the peaks at 2.67 eV (464 nm) for Pm (3) over barm phase, 5.21 eV (238 nm) for Pmn2(1) phase and 2.63 eV (471 nm) for Pmmn phase. Pm (3) over barm and Pmmn phases correspond to the visible region. The absorption peaks are getting wider and have higher magnitude from Pm (3) over barm to Pmmn phase. The optical conductivity for the cubic structure with Pm (3) over barm phase was found to be higher than orthorhombic structures with Pmn2(1), and Pmmn phases. The reflectivity maxima decrease from Pm (3) over barm to Pmn2(1)