MgB2: Superconductivity and Pressure

2003 ◽  
Vol 17 (21) ◽  
pp. 3785-3806 ◽  
Author(s):  
A. K. M. A. Islam ◽  
F. N. Islam

The present work is an overview of the properties of the newly discovered MgB 2 carried out by us using first-principles density functional calculations as implemented in a program package, not used by other workers. Structural, bonding and elastic properties, phonon coupling, transition temperature, electronic band structure, density of states, charge-density and chemical bonding, electric field gradient are all considered for the new material at ambient and at higher pressures. New and interesting aspects including the pressure-induced structural phase transition in MgB 2 are also discussed. The calculations are compared with the available results and their implications are discussed which may help in understanding some key issues.

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1445
Author(s):  
Tahani A. Alrebdi ◽  
Mohammed Benali Kanoun ◽  
Souraya Goumri-Said

We investigated structure optimization, mechanical stability, electronic and bonding properties of the nanolaminate compounds Ti2PbC, Zr2PbC, and Hf2PbC using the first-principles calculations. These structures display nanolaminated edifices where MC layers are interleaved with Pb. The calculation of formation energies, elastic moduli and phonons reveal that all MAX phase systems are exothermic, and are intrinsically and dynamically stable at zero and under pressure. The mechanical and thermal properties are reported with fundamental insights. Results of bulk modulus and shear modulus show that the investigated compounds display a remarkable hardness. The elastic constants C11 and C33 rise more quickly with an increase in pressure than that of other elastic constants. Electronic and bonding properties are investigated through the calculation of electronic band structure, density of states, and charge densities.


2021 ◽  
Author(s):  
O. T. Uto ◽  
J. O. Akinlami ◽  
S. Kenmoe ◽  
G. A. Adebayo

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.


2009 ◽  
Vol 23 (32) ◽  
pp. 5929-5934 ◽  
Author(s):  
T. JEONG

The electronic band structure of LuPd 2 Si 2 was studied based on the density functional theory within local density approximation and fully relativistic schemes. The Lu 4f states are completely filled and have flat bands around -5.0 eV. The fully relativistic band structure scheme shows that spin–orbit coupling splits the 4f states into two manifolds, the 4f7/2 and the 4f5/2 multiplet.


2017 ◽  
Vol 95 (8) ◽  
pp. 691-698
Author(s):  
Y. Mogulkoc ◽  
Y.O. Ciftci ◽  
G. Surucu

Using the first-principles calculations based on density functional theory (DFT), the structural, elastic, electronic, and vibrational properties of LiAl have been explored within the generalized gradient approximation (GGA) using the Vienna ab initio simulation package (VASP). The results demonstrate that LiAl compound is stable in the NaTl-type structure (B32) at ambient pressure, which is in good agreement with the experimental results and there is a structural phase transition from NaTl-type structure (B32) to CsCl-type structure (B2) at around 22.2 GPa pressure value. The pressure effects on the elastic properties have been discussed and the elastic property calculation indicates that the elastic instability could provide a phase transition driving force according to the variations relation of the elastic constant versus pressure. To gain further information about this, we also have investigated the other elastic parameters (i.e., Zener anisotropy factor, Poisson’s ratio, Young’s modulus, and isotropic shear modulus). The electronic band structure, total and partial density of states, phonon dispersion curves, and one-phonon density of states of B2 and B32 phases are also presented with results.


2012 ◽  
Vol 488-489 ◽  
pp. 129-132 ◽  
Author(s):  
C. Kanagaraj ◽  
Baskaran Natesan

We have performed detailed structural, electronic and magnetic properties of high - TC multiferroic CuO using first principles density functional theory. The total energy results revealed that AFM is the most stable magnetic ground state of CuO. The DOS and electronic band structure calculations show that in the absence of on-site Coulomb interaction (U), AFM structure of CuO heads to a metallic state. However, upon incorporating U in the calculations, a band gap of 1.2 eV is recovered. Furthermore, the Born effective charges calculated on Cu does not show any anomalous character.This suggests that the polarization seen in CuO could be attributed to the spin induced AFM ordering effect.


2020 ◽  
Vol 17 (2) ◽  
pp. 149
Author(s):  
Nurakma Natasya Md Jahangir Alam ◽  
Nur Aisyah Ab Malik Marwan ◽  
Mohd Hazrie Samat ◽  
Muhammad Zamir Mohyedin ◽  
Nur Hafiz Hussin ◽  
...  

Works are centered on exploring lead-free ferroelectric materials that have a comparable unique ns2 solitary pair electrons with Pb (II), for example, Sn (II) using the first-principles study. All counts were performed dependent on Density Functional Theory (DFT) that has been executed in CASTEP. GGA-PBE displays the most exact qualities for cross-section parameters concerning exploratory qualities for both cubic PbTiO3. In the interim, GGA-PBEsol functional is exact for tetragonal PTO. The electronic band structure and density of states show the presence of hybridizations between anion O 2p and cation Pb 6s/Sn 5s unique solitary pair in tetragonal PTO and SnTO stage.


2019 ◽  
Vol 33 (07) ◽  
pp. 1950045
Author(s):  
R. Mahdjoubi ◽  
Y. Megdoud ◽  
L. Tairi ◽  
H. Meradji ◽  
Z. Chouahda ◽  
...  

First-principles calculations of the structural, electronic, optical and thermal properties of chalcopyrite CuXTe2 (X[Formula: see text]=[Formula: see text]Al, Ga, In) have been performed within density functional theory using the full-potential linearized augmented plane wave (FP-LAPW) method, by employing for the exchange and correlation potential the approximations WC-GGA and mBJ-GGA. The effect of X cations replacement on the structural, electronic band structure, density of states and optical properties were highlighted and explained. Our results are in good agreement with the previous theoretical and experimental data. As far as we know, for the first time we find the effects of temperature and pressure on thermal parameters of CuAlTe2 and CuGaTe2 compounds. Thermal properties are very useful for optimizing crystal growth, and predict photovoltaic applications on extreme thermodynamic conditions.


2014 ◽  
Vol 28 (10) ◽  
pp. 1450077 ◽  
Author(s):  
Asif Mahmood ◽  
Shahid M. Ramay ◽  
Hafiz Muhammad Rafique ◽  
Yousef Al-Zaghayer ◽  
Salah Ud-Din Khan

In this paper, first-principles calculations of structural, electronic, optical and thermoelectric properties of AgMO 3 ( M = V , Nb and Ta ) have been carried out using full potential linearized augmented plane wave plus local orbitals method ( FP - LAPW + lo ) and BoltzTraP code within the framework of density functional theory (DFT). The calculated structural parameters are found to agree well with the experimental data, while the electronic band structure indicates that AgNbO 3 and AgTaO 3 are semiconductors with indirect bandgaps of 1.60 eV and 1.64 eV, respectively, between the occupied O 2p and unoccupied d states of Nb and Ta . On the other hand, AgVO 3 is found metallic due to the overlapping behavior of states across the Fermi level. Furthermore, optical properties, such as dielectric function, absorption coefficient, optical reflectivity, refractive index and extinction coefficient of AgNbO 3 and AgTaO 3, are calculated for incident photon energy up to 50 eV. Finally, we calculate thermo power for AgNbO 3 and AgTaO 3 at fixed doping 1019 cm-3. Electron doped thermo power of AgNbO 3 shows significant increase over AgTaO 3 with temperature.


RSC Advances ◽  
2015 ◽  
Vol 5 (56) ◽  
pp. 44960-44968 ◽  
Author(s):  
A. H. Reshak

Using the density functional theory plus Hubbard Hamiltonian we have investigated the spin up/down electronic band structure, density of states, electronic charge density distribution and the dispersion of the optical properties of microcrystalline β-RbNd(MoO4)2.


2017 ◽  
Vol 31 (08) ◽  
pp. 1750044 ◽  
Author(s):  
Mosayeb Naseri ◽  
Jafar Jalilian ◽  
A. H. Reshak

The electronic and optical properties of pentagonal B2C (penta-B2C) monolayer are investigated by means of the first-principles calculations in the framework of the density functional theory. The cohesive energy consideration confirms the good stability of the B2C nanostructure in this phase. The electronic band structure reveals that the valence band maximum (VBM) is located at [Formula: see text]-point of the first Brillouin zone (BZ) whereas the conduction band minimum (CBM) is situated at the center of the BZ, resulting in an indirect energy bandgap of about 1.5 eV. Furthermore, a calculated low absorption and low reflection of the material in low energy ranges denote the transparency of the B2C monolayer in the investigated range for normal light incidence. The obtained results may find application in fabrication of future opto-electronic devices.


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