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First-principles study of zinc-blende to rocksalt phase transition in BN

100%
Cui S., Feng W., Hu H., Feng Z.
Open Physics
|
2010
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vol. 8
|
issue 4
628-633
EN
The structural, electronic and elastic properties of the cubic boron nitride (BN) compound are investigated by a first-principle pseudopotential method. The calculations show that the structural phase transition from the zinc-blende(ZB) structure to the rocksalt (RS) structure occurs at a transition pressure of 1088 GPa and with a volume reduction of 3.1%. Both the ZB and RS structures of BN have indirect gaps, with energy gaps of 4.80 eV and 2.11 eV, respectively. The positive pressure derivative of the indirect band gap (Γ-X) energy for the the ZB phase and the predicted ultrahigh metallization pressure are attributed to the absence of d occupations in the valence bands. The increase of the shear modulus with increasing pressure implies that the lattice stability becomes higher when BN is compressed.
2
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Elastic Anisotropic and Thermodynamic Properties of Two BC₇ Phases

100%
Xing M., Li B., Yu Z., Chen Q.
Acta Physica Polonica A
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2017
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vol. 132
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issue 4
1340-1346
EN
The structural, elastic, anisotropic, and thermodynamic properties of P3m1-BC₇ and Pmm2-BC₇ have been studied in this paper utilizing first-principles calculations. In comparison with the elastic properties of Pmm2-BC₇, P3m1-BC₇ exhibits slightly higher values in bulk modulus and B/G, with similar values in shear modulus, the Young modulus, and the Poisson ratio. The calculated Pugh modulus ratio (B/G) and the Poisson ratio demonstrates P3m1-BC₇ from brittle to ductile at 93.60 and 93.73 GPa, respectively. Calculations of shear anisotropic factor, universal elastic anisotropy index, shear modulus, the Young modulus, and the Poisson ratio for BC₇ then demonstrate that Pmm2-BC₇ exhibits a larger elastic anisotropy than P3m1-BC₇. Quasi-harmonic Debye model is finally applied to investigate the Debye temperature, the coefficient of thermal expansion, heat capacity and Grüneisen parameter of Pmm2-BC₇ and P3m1-BC₇.
3
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Investigations of Structural, Elastic, Electronic, Magnetic and Transport Properties of the Heusler Compounds Zr₂PdZ (Z = Al, Ga, and In): FP-LAPW Method

88%
Khelfaoui F., Boudali A., Bentayeb A., El Hachemi Omari L., Si Abderrahmane Y.
Acta Physica Polonica A
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2018
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vol. 133
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issue 1
157-163
EN
Structural, elastic, electronic, magnetic and thermoelectric properties of the Heusler compounds: Zr₂PdAl, Zr₂PdGa, and Zr₂PdIn are performed using generalized gradient approximation with exchange-correlation function of the Perdew-Burke-Ernzerhof. The elastic constants are calculated at P=0 GPa. From the obtained elastic parameters, it is inferred that these compounds, with the Hg₂TiCu-type structure, are elastically stable and ductile in nature. The calculated density of states, magnetic moments and band structure are also given. The band structures of these compounds reveal that all of them have almost half metallic character with the narrow indirect band gap in the minority spin channel that amounts to 0.36, 0.46, and 0.40 eV for Zr₂PdAl, Zr₂PdGa, and Zr₂PdIn, respectively. The total spin magnetic moments (M_{tot}) of the considered compounds are very close to integer value 3, which satisfies a Slater-Pauling type rule for localized magnetic moment systems M_{tot}=Z_{T}-18, where Z_{T}=21 is the number of valence electrons in the primitive cell. The thermoelectric properties of these materials are discussed on the basis of the Seebeck coefficients, electrical and thermal conductivity relative to relaxation time as a function of temperature, at the Fermi level, using the Boltzmann transport theory. After several browse in the literature, the obtained results are the first predictions of the physical properties for the inverse full-Heusler compounds Zr₂PdZ (Z = Al, Ga and In).
4
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Fullerenes patched by flowers

88%
Pop R., Medeleanu M., Diudea M., Szefler B., Cioslowski J.
Open Chemistry
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2013
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vol. 11
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issue 4
527-534
EN
Stability measures, such as the total energy and the HOMO-LUMO gap, calculated at the Hartree-Fock and DFT levels of theory, and the aromatic character of five circulenes/flowers with a hexagonal core and petals consisting of 5-, 6- and 7-membered rings are investigated. Geometric (HOMA) and magnetic (NICS) criteria are used to estimate the local aromatic character of every ring of the investigated circulenes. The local aromaticity of the coronene and sumanene patches in two tetrahedrally spanned fullerenes were calculated and compared with the HOMA and NICS values of the corresponding isolated circulenes. [...]
5
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A Novel Theoretical Study of Elastic and Electronic Properties of M₂CdC (M = Zr, Hf, and Ta) MAX Phases

75%
Mebrek M., Mokaddem A., Doumi B., Yakoubi A., Mir A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 1
76-81
EN
In this study, we have investigated the structural, electronic, and elastic properties of the M₂CdC (M = Ta, Zr, and Hf) MAX phases, using the first-principle methods based on the density functional theory. The calculated formation energies revealed that these compounds are thermodynamically stable in the hexagonal MAX phase. The stability is confirmed by the elastic constants and the conditions of mechanical stability criterion. Also, we have determined the bulk and shear modules of the Young modulus and the Poisson coefficient. The band structures indicate that the three materials are electrically conductive. The chemical bond in M₂CdC is covalent-ionic in nature with the presence of metallic character. For the density of states the hybridization peak between M d and C p occurs in the lower energy range. We have found that there is no gap for these materials due to the existence of a maximum peak of DOS around Fermi level.
6
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Structural and Electronic Properties of the BN, BP and BAs in the Different Phases of Zinc-Blende, NaCl and CsCl

75%
Bencherif K., Yakoubi A., Mebtouche H.
Acta Physica Polonica A
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2017
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vol. 131
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issue 2
209-212
EN
In this work we used the first ab initio calculations to study the stability of the binary alloys BN, BP and BAs and their behavior in the different phases of zinc-blende, Nacl and CsCl. The full potential linearized augmented plane wave method was employed within density functional theory. Our results show the difference in the calculated structural properties and the band structure is obtained for the zinc-blende structure. We have investigated the lattice parameters and band gap energies. We also give the valence charge density at a high pressure and the analysis of the density of states.
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