scholarly journals High-pressure structural phase transitions, electronic properties, and intermediate states of CaSe

2019 ◽  
Vol 97 (7) ◽  
pp. 797-802
Author(s):  
Cihan Kürkçü
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Density Functional ◽  
Structural Phase ◽  
Ambient Conditions ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Space Group ◽  
Structure Space ◽  
Intermediate States

In this study, ab initio calculations have been carried out to understand the effect of extreme external pressure on the crystal structure of CaSe. The crystal structure of CaSe, a calcium chalcogen, is studied using density functional theory (DFT) with the generalized gradient approximation (GGA) up to 250 GPa under high hydrostatic pressure. Structurally CaSe crystallizes in cubic NaCl-type (B1) structure (space group: [Formula: see text]) at ambient conditions. The results indicated that CaSe undergoes a structural phase transition from this cubic structure to another cubic CsCl-type (B2) structure (space group: [Formula: see text]) at high pressure. This transformation is based on two intermediate states with space group [Formula: see text] and C2/m. Additionally, the electronic band structures and density of states for the obtained B1 and B2 structures of CaSe have been calculated. According to these calculations, obtained band gap values are in good agreement with the values reported in the literature.

scholarly journals Investigation of the structural and electronic properties of CdS under high pressure: an ab initio study

2018 ◽  
Vol 96 (2) ◽  
pp. 216-224 ◽  
Author(s):  
C. Yamcicier ◽  
Z. Merdan ◽  
C. Kurkcu
Keyword(s):  
Phase Transition ◽  
Ab Initio ◽  
Density Functional ◽  
Structural Phase ◽  
Type Structure ◽  
Ambient Conditions ◽  
Space Group ◽  
Space Groups ◽  
Intermediate States ◽  
Calculation Results

An ab initio constant pressure study is carried out to explore the behaviour of cadmium sulfide (CdS) under high hydrostatic pressure. We have studied the structural properties of CdS using density functional theory (DFT) under pressure up to 200 GPa. CdS crystallizes in a wurtzite (WZ)-type structure under ambient conditions. CdS undergoes a structural phase transition from the hexagonal WZ-type structure with space group P63mc to cubic NaCl-type structure with space group [Formula: see text]. Another phase transition is obtained from NaCl-type structure to the orthorhombic CdS-III-type structure with space group Pmmn. The first transformation proceeds via seven intermediate states with space group Cmc21, P21, Pmn21, P21/m, Pmmn, I4/mmm, and Cmcm. The latter transformation is based on two intermediate states with space groups Immm and P21/m. These phase transitions are also studied by total energy and enthalpy calculations. According to these calculations, the phase transformations occur at about 3 and 51 GPa, respectively. Calculation results on the other basic properties, such as lattice constant, volume, and bulk modulus are also compared with those of other recent theoretical and experimental data, and generally, good agreement with the available data are obtained.

scholarly journals Electronic structure, Mechanical and Thermodynamic properties of CoYSb (Y= Cr, Mo, W) half-Heusler compounds as potential spintronic materials

2021 ◽  
Author(s):  
O. T. Uto ◽  
J. O. Akinlami ◽  
S. Kenmoe ◽  
G. A. Adebayo
Keyword(s):  
Density Functional ◽  
Electronic Band Structure ◽  
Structural Phase ◽  
Covalent Bond ◽  
Stable Phase ◽  
Type I ◽  
Generalized Gradient ◽  
Electronic Density ◽  
Electronic Band ◽  
Half Metallic

Abstract The CoYSb (Y = Cr, Mo and W) compounds which are XYZ type half-Heusler alloys and also exist in the face centred cubic MgAgAs-type struc-ture conform to F ̄43m space group. In the present work, these compoundsare investigated in different atomic arrangements called, Type-I, Type-II andType-III phases, using Generalized Gradient Approximation (GGA) in the Density Functional Theory (DFT) implemented in QE (Quantum EspressoAb-Initio Simulation Package). The ferromagnetic state of these alloys is studied after investigating their stable structural phase. The calculated electronic band structure and the total electronic density of states indicated nearly half-metallic behaviour in CoMoSb with a possibility of being used in spintronic application, metallic in CoWSb and half-metallic in CoCrSb, with the minority spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behaviour of these alloys in the stable phase. Finally, due to its high Debye temperature value, CoCrSb possesses a stronger covalent bond than CoMoSb and CoWSb, respectively.

scholarly journals High Pressure Study of Structural and Electronic Properties of PbSe

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
P. Bhambhani ◽  
K. Kabra ◽  
B. K. Sharma ◽  
G. Sharma
Keyword(s):  
High Pressure ◽  
Electronic Properties ◽  
Energy Gap ◽  
Electronic Band Structure ◽  
Local Density ◽  
Structural Phase ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Structural And Electronic Properties ◽  
Direct Band

High pressure structural phase transition and electronic properties have been investigated using the linear combination of atomic orbitals (LCAO) method with two exchange-correlation approximations, the generalized gradient approximation (GGA) and local density approximation (LDA). The present study shows phase transitions from B1 to B27 and B27 to B2 at 6.24 GPa and 16.39 GPa, respectively. Lattice constant, bulk modulus, and energy gap of pressure-induced PbSe are found to be in good agreement with previous theoretical and experimental results. Variation of electronic band structure with pressure shows direct band gap along L point of the Brillouin zone.

scholarly journals Density functional studies of magneto-optic properties of Sr2GdReO6

2018 ◽  
Vol 4 (1) ◽  
pp. 13-19 ◽  
Author(s):  
Saadi Berri ◽  
Sabah Chami ◽  
Mourad Attallah ◽  
Mouloud Oumertem ◽  
Djamel Maouche
Keyword(s):  
Density Functional ◽  
Interaction Mechanism ◽  
Double Perovskite ◽  
Full Potential ◽  
Ambient Conditions ◽  
Generalized Gradient ◽  
Half Metallicity ◽  
Double Exchange Interaction ◽  
Electronic Band ◽  
Magneto Optic

The electronic structure and magneto-optic properties of the Sr2GdReO6 double perovskite were investigated using the full-potential linearized augmented plane wave (FPLAPW) method. Exchange correlation effects are treated using the generalized gradient approximations GGA, GGA + U and GGA + U + SOC approachs. At ambient conditions, these calculation predict a half-metallic character for Sr2GdReO6 material. The electronic band structures and density of states demonstrate that Sr2GdReO6 is HM with a magnetic moment of 9 µB/fu and HM flip gap of 1.82 eV. The half metallicity is attributed by the double-exchange interaction mechanism via the Gd(4f)–O(2p)–Re(t2g) π-bounding. These new double perovskite may become ideal candidate material for future spintronic applications. The analysis charge densities show that bonding character as a mixture of covalent and ionic nature. The optical properties are analyzed and the origin of some peaks in the spectra is described. Besides, the dielectric function ε(ω), refractive index n (ω) and extinction coefficient K (ω) for radiation up to 14 eV have also been reported.

scholarly journals Pressure-induced Pb–Pb bonding and phase transition in Pb2SnO4

2020 ◽  
Vol 76 (6) ◽  
pp. 979-991
Author(s):  
Dominik Spahr ◽  
Michał Stękiel ◽  
Dominik Zimmer ◽  
Lkhamsuren Bayarjargal ◽  
Katja Bunk ◽  
...  
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
High Pressure ◽  
Powder Diffraction ◽  
Density Functional ◽  
Structural Phase ◽  
Irreducible Representations ◽  
Ambient Conditions ◽  
Functional Theory ◽  
Electron Pairs

High-pressure single-crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator-to-semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory-based calculations show that at ambient conditions the channels in the structure host the stereochemically-active Pb 6s 2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.

Preparation, Crystal Structure, Properties, and Electronic Band Structure of TlTaSe3

2005 ◽  
Vol 60 (8) ◽  
pp. 858-866 ◽  
Author(s):  
Christoph L. Teske ◽  
Wolfgang Bensch ◽  
Diana Benea ◽  
Jan Minár ◽  
Alexander Perlov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Band Structure ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Molar Ratio ◽  
Orthorhombic Space Group ◽  
Electronic Band ◽  
Space Group ◽  
Orthorhombic Modification ◽  
Characteristic Features

TlTaSe3 was prepared from a fused mixture of Tl4Ta2Se11, Ta and Se in the molar ratio 1:2:1. The compound shows dimorphism with H-TlTaSe3, hexagonal, space group P63/mmc, a = 7.2436(6), c = 5.9736(6) Å , c/a = 1.213 and O-TlTaSe3, orthorhombic, space group Pnma, a = 9.554(13), b = 3.6244(6), c=14.7271(17) Å . The crystal structure of H-TlTaSe3 is isotypic to BaVSe3 whereas that of O-TlTaSe3 is closely related to the NH4CdCl3-type. Characteristic features of the structures are: 1∞[TaSe32−] chains of regular octahedra sharing faces along [001] for the hexagonal form and columns of double edge-sharing octahedra 1∞[Ta2Se62−] running along [010] for O-TlTaSe3. The columns are each separated by Tl+ ions with the coordination number CN = 12 and CN = 8 respectively. The structures are compared and discussed in context with other isotypic structures of chalcogenides. The orthorhombic modification O-TlTaSe3 is a semiconductor while H-TlTaSe3 shows conventional metallic behaviour. The electronic structures of both modifications are discussed on the base of band structure calculations performed within the framework of density functional theory.

Ab initio calculation on the Optical Properties of AA- Stacked two dimensional Graphene, Silicene, Germanene, and Stanene

2018 ◽  
Vol 1 (1) ◽  
pp. 46-50
Author(s):  
Rita John ◽  
Benita Merlin
Keyword(s):  
Optical Properties ◽  
Band Structure ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Complex Refractive Index ◽  
Single Layer ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Wide Range ◽  
Optical Region

In this study, we have analyzed the electronic band structure and optical properties of AA-stacked bilayer graphene and its 2D analogues and compared the results with single layers. The calculations have been done using Density Functional Theory with Generalized Gradient Approximation as exchange correlation potential as in CASTEP. The study on electronic band structure shows the splitting of valence and conduction bands. A band gap of 0.342eV in graphene and an infinitesimally small gap in other 2D materials are generated. Similar to a single layer, AA-stacked bilayer materials also exhibit excellent optical properties throughout the optical region from infrared to ultraviolet. Optical properties are studied along both parallel (||) and perpendicular ( ) polarization directions. The complex dielectric function (ε) and the complex refractive index (N) are calculated. The calculated values of ε and N enable us to analyze optical absorption, reflectivity, conductivity, and the electron loss function. Inferences from the study of optical properties are presented. In general the optical properties are found to be enhanced compared to its corresponding single layer. The further study brings out greater inferences towards their direct application in the optical industry through a wide range of the optical spectrum.

scholarly journals Crystal Structures of New Ivermectin Pseudopolymorphs

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 172
Author(s):  
Kirill Shubin ◽  
Agris Bērziņš ◽  
Sergey Belyakov
Keyword(s):  
Crystal Structure ◽  
Molecular Conformation ◽  
Methyl Tert Butyl Ether ◽  
Minor Role ◽  
Scanning Calorimetry ◽  
Orthorhombic Crystal ◽  
Monoclinic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Space Group ◽  
Structure Space

New pseudopolymorphs of ivermectin (IVM), a potential anti-COVID-19 drug, were prepared. The crystal structure for three pseudopolymorphic crystalline forms of IVM has been determined using single-crystal X-ray crystallographic analysis. The molecular conformation of IVM in crystals has been compared with the conformation of isolated molecules modeled by DFT calculations. In a solvent with relatively small molecules (ethanol), IVM forms monoclinic crystal structure (space group I2), which contains two types of voids. When crystallized from solvents with larger molecules, like γ-valerolactone (GVL) and methyl tert-butyl ether (MTBE), IVM forms orthorhombic crystal structure (space group P212121). Calculations of the lattice energy indicate that interactions between IVM and solvents play a minor role; the main contribution to energy is made by the interactions between the molecules of IVM itself, which form a framework in the crystal structure. Interactions between IVM and molecules of solvents were evaluated using Hirshfeld surface analysis. Thermal analysis of the new pseudopolymorphs of IVM was performed by differential scanning calorimetry and thermogravimetric analysis.

scholarly journals (R)-Baclofen [(R)-4-amino-3-(4-chlorophenyl)butanoic acid]

2022 ◽  
Vol 78 (1) ◽  
Author(s):  
Feodor Belov ◽  
Alexander Villinger ◽  
Jan von Langermann
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Single Crystal ◽  
Title Compound ◽  
Single Crystal Xrd ◽  
Butanoic Acid ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Space Group ◽  
Structure Space

This article provides the first single-crystal XRD-based structure of enantiopure (R)-baclofen (form C), C10H12ClNO2, without any co-crystallized substances. In the enantiopure title compound, the molecules arrange themselves in an orthorhombic crystal structure (space group P212121). In the crystal, strong hydrogen bonds and C—H ... Cl bonds interconnect the zwitterionic molecules.

DFT study of pressure effects in molecular crystal 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo-[5.5.0.05,903,11]-dodecane

2014 ◽  
Vol 92 (7) ◽  
pp. 616-624 ◽  
Author(s):  
Zhichao Liu ◽  
Qiong Wu ◽  
Weihua Zhu ◽  
Heming Xiao
Keyword(s):  
High Pressure ◽  
Energy Loss ◽  
Loss Function ◽  
Density Functional ◽  
Pressure Range ◽  
Blue Shift ◽  
Pressure Effects ◽  
Ambient Conditions ◽  
Energy Loss Function ◽  
Electron Transitions

Density functional theory was used to study the structural, electronic, and optical properties of crystalline 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo-[5.5.0.05,903,11]-dodecane (TEX) under hydrostatic pressure. The results indicate that there is a displacive transition in TEX under compression that has never been found in experiments. As the pressure increases, the band gap gradually decreases but presents an abnormal increase at 61 GPa, called the structural transition; moreover, the gap reduction is more pronounced in the low-pressure range compared with the high-pressure range. An analysis of density of states shows that the electronic delocalization in TEX is enhanced gradually under the influence of pressure. The peaks of the imaginary parts of the dielectric functions, energy-loss function, and reflectivity may come mainly from the electron transitions between the oxygen 2p and nitrogen 2p states. The electron energy-loss function presents a blue shift under compression. TEX has relatively higher optical activity at high pressure than at ambient conditions.

Sign in / Sign up

Export Citation Format

Share Document