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Start Over Descriptor "Phonon Spectrum" Topic ab initio
8 results on '"Phonon Spectrum"'

1. Structure and Lattice Dynamics of R2Sn2O7 and R2Zr2O7 (R = La–Lu) Crystals: Ab Initio Calculation.

Author

Chernyshev, V. A., Glukhov, K. I., and Agzamova, P. A.

Subjects
*LATTICE dynamics, *AB-initio calculations, *HARTREE-Fock approximation, *ZIRCONIUM oxide, *CRYSTALS, *RARE earth oxides
Abstract

Crystal structure and phonon spectrum of rare-earth stannates R 2 Sn 2 O 7 and zirconates R 2 Zr 2 O 7 (R = La–Lu) with the pyrochlore structure were studied within the framework of DFT and MO LCAO approach. The calculations were performed by using hybrid functional PBE0 that take into account nonlocal exchange at the Hartree-Fock formalism. The calculation of the phonon spectrum at the Γ -point made it possible to supplement the available experimental data on the IR and Raman spectra of stannates and zirconates. In the framework of the ab initio approach, the change of the elastic properties of zirconium oxide t-ZrO 2 by doping the yttrium was studied. Calculations were performed in the CRYSTAL17 program designed to simulate periodic structures. [ABSTRACT FROM AUTHOR]

Published
2022
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2. Structure and Lattice Dynamics of La2Zr2O7 Crystal: Ab Initio Calculation

Author

Chernyshev, V. A., Hutchison, David, Editorial Board Member, Kanade, Takeo, Editorial Board Member, Kittler, Josef, Editorial Board Member, Kleinberg, Jon M., Editorial Board Member, Mattern, Friedemann, Editorial Board Member, Mitchell, John C., Editorial Board Member, Naor, Moni, Editorial Board Member, Pandu Rangan, C., Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Terzopoulos, Demetri, Editorial Board Member, Tygar, Doug, Editorial Board Member, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Misra, Sanjay, editor, Gervasi, Osvaldo, editor, Murgante, Beniamino, editor, Stankova, Elena, editor, Korkhov, Vladimir, editor, Torre, Carmelo, editor, Rocha, Ana Maria A.C., editor, Taniar, David, editor, Apduhan, Bernady O., editor, and Tarantino, Eufemia, editor

Published
2019
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4. Ab-initio calculations of semiconductor MgGeP2 and MgGeAs2.

Author

Kocak, B. and Ciftci, Y.O.

Subjects
*AB-initio calculations, *DENSITY functional theory, *MOLECULAR dynamics calculations, *PHONON spectra, *ELECTRON energy loss spectroscopy
Abstract

In this study, we focus on structural, electronic, elastic, lattice dynamic and optic properties of MgGeP 2 and MgGeAs 2 using ab-initio density-functional theory (DFT) within Armiento-Mattson 2005 (AM05) scheme of the generalized gradient approximation (GGA) for the exchange-correlation potential. Our computed structural results are in reasonable agreement with the literature. The band gap of these compounds is predicted to be direct. Our elastic results prove that these compounds are mechanically stable. The obtained phonon spectra of MgGeP 2 and MgGeAs 2 do not exhibit any significant imaginary branches using GGA-AM05 for the exchange-correlation approximation. Further analysis of the optical response of the dielectric functions, optical reflectivity, refractive index, extinction coefficient and electron energy loss delves into for the energy range of 0–22.5 eV. It motivated that there exists an optical polarization anisotropy of these compounds for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Published
2016
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5. Electronic and thermodynamic properties of lanthanum tetraboride on low-temperature experimental and ab-initio calculation data

Author

A. V. Matovnikov, N. V. Mitroshenkov, H.B. Ozisik, I.R. Shein, Engin Deligoz, V. V. Novikov, A. V. Morozov, Gokhan Surucu, Sabire Yazıcı Fen Edebiyat Fakültesi, OpenMETU, Kaman Meslek Yüksekokulu, and Gökhan Sürücü / 0000-0002-3910-8575

Subjects
Materials science, Thermodynamic Properties, Phonon, Ab initio, Thermodynamics, chemistry.chemical_element, 02 engineering and technology, First-principles Calculations, Tetraborides, 010402 general chemistry, 01 natural sciences, Heat capacity, Low Temperature, Lattice (order), Phonon Spectrum, Materials Chemistry, Lanthanum, Electronic band structure, Electronic Properties, Mechanical Engineering, Metals and Alloys, Fermi surface, Grüneisen parameter, 021001 nanoscience & nanotechnology, 0104 chemical sciences, chemistry, Mechanics of Materials, 0210 nano-technology
Abstract

*Özışık, Hacı ( Aksaray, Yazar ) *Deligöz, Engin ( Aksaray, Yazar ), The characteristics of the electronic and phonon subsystems of lanthanum tetraboride (LaB4) studied using first-principles calculations. The calculated lattice parameters, as well as the positions of atomic, are satisfactorily consistent with the experimental data. The partial densities of states, band structure, Fermi surface, phonon dispersion curve of LaB4 are calculated and analysed. The reliability of the calculation results is confirmed by a satisfactory agreement between the calculated thermodynamic parameters of LaB4 (temperature changes in heat capacity, entropy, Gruneisen parameter and volume modulus) with experimental data.

Published
2021

6. Ab initio study of the high-pressure phases and dynamical properties of ZnAl2O4 and ZnGa2O4.

Author

López-Moreno, S., Romero, A.H., Rodríguez-Hernández, P., and Muñoz, A.

Subjects
*SPINEL, *GEMS & precious stones, *PHONONS, *QUASIPARTICLES, *SPECTRUM analysis, *HIGH pressure (Technology)
Abstract

In this paper, we report ab initio calculations of the vibrational and structural properties of ZnAl2O4 and ZnGa2O4 spinel structures. The calculated vibrational modes at zero pressure, at the Γ point and the complete phonon spectrum of both compounds are presented. Also, we report our findings for the high-pressure structure dependences of spinel and post-spinel structures. [ABSTRACT FROM AUTHOR]

Published
2009
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7. Phonon spectrum of Nd2Zr2O7 crystal: ab initio calculation

Author

V. A. Chernyshev

Subjects
Nuclear and High Energy Physics, Materials science, Phonon, Spectrum (functional analysis), Ab initio, DFT, Molecular physics, Atomic and Molecular Physics, and Optics, PHONON SPECTRUM, Electronic, Optical and Magnetic Materials, Hybrid functional, Crystal, HYBRID FUNCTIONALS, PYROCHLORES, Density functional theory, Spectroscopy
Abstract

Crystal structure and phonon spectrum of rare-earth pyroclore oxide Nd2Zr2O7 were studied within the framework of density functional theory and MO LKAO approach. The calculations were performed by using hybrid functionals that take into account both local and nonlocal (at the Hartree-Fock formalism) exchanges. Calculations were performed with the functionals PBESOL0 and PBE0. The fundamental vibration frequencies of Nd2Zr2O7 were calculated. The calculations were performed in the CRYSTAL17 program designed to simulate periodic structures. © Kazan Federal University (KFU). Ministry of Education and Science of the Russian Federation, Minobrnauka: 3.9534.2017/8.9 This study was supported by the Ministry of Education and Science of the Russian Federation (project No. 3.9534.2017/8.9).

Published
2019
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8. Lattice Dynamics Study of Phonon Instability and Thermal Properties of Type-I Clathrate K8Si46 under High Pressure

Author

Zhao Yi Zeng, Wei Zhang, Zhi-Guo Li, and Ni Na Ge

Subjects
clathrate compounds, Phase transition, Phonon, phonon spectrum, Clathrate hydrate, Ab initio, 02 engineering and technology, 01 natural sciences, Instability, lcsh:Technology, Thermal expansion, Condensed Matter::Materials Science, Lattice (order), 0103 physical sciences, General Materials Science, 010306 general physics, lcsh:Microscopy, lcsh:QC120-168.85, Condensed matter physics, lcsh:QH201-278.5, Chemistry, lcsh:T, 021001 nanoscience & nanotechnology, high pressure, lcsh:TA1-2040, lattice dynamics, Density of states, lcsh:Descriptive and experimental mechanics, lcsh:Electrical engineering. Electronics. Nuclear engineering, 0210 nano-technology, lcsh:Engineering (General). Civil engineering (General), lcsh:TK1-9971
Abstract

For a further understanding of the phase transitions mechanism in type-I silicon clathrates K₈Si46, ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate under pressure within the framework of density functional perturbation theory. Our lattice dynamics simulation results showed that the pressure induced phase transition of K₈Si46 was believed to be driven by the phonon instability of the calthrate lattice. Analysis of the evolution of the partial phonon density of state with pressure, a legible dynamic picture for both guest K atoms and host lattice, was given. In addition, based on phonon calculations and combined with quasi-harmonic approximation, the specific heat of K₈Si46 was derived, which agreed very well with experimental results. Also, other important thermal properties including the thermal expansion coefficients and Gruneisen parameters of K₈Si46 under different temperature and pressure were also predicted.

Published
2016

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