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Rashid Vali

Vice President for Education and Postgraduate Studies and Professor of Condensed Matter Physics

Biography

Dr. Vali was born in Bojnourd, North Khorasan, Iran. He received undergraduate degrees in applied physics (Solid State Physics) from Shahid Beheshti University, Tehran, Iran (1992) and in Solid State Physics from Tabriz University, East Azerbaijan, Iran (1994). He earned a Ph.D. in Theoretical Condensed Matther Physics from Ferdowsi University of Mashhad, Khorasan-E-Razavi, Iran (2004). He then held faculty position at the Damghan University, Semnan, Iran. 

His Administrative portfolio includes but doesn't limited to dean of school of physics, and vice president for administrative and financial affairs. He is currently vice president for education and postgraduate studies from 2016  and full professor of condensed matter physics in Damghan university.

His research area lies in the field of Investigation of electronic, dynamical and dielectric properties of materials, using density functional theory and density functional perturbation theory; Quantum transport in mesoscopic systems; Topological Insulators; Spintronics; Nanoelectronics;

 

Selected Publications

Book:

  1. Vali, Quantum transport in conductor/superconductor junction structures on the surface of Topological Insulators, Damghan University Press, 2015.

Journal Papers

Vali, R. First principles phonon calculations of dielectric properties in Ba2MWO6 (M = Mg, Zn) (2016) 122, pp. 146-149. Cited 1 time.

DOI: 10.1016/j.commatsci.2016.05.017

The vibrational and dielectric properties of the double perovskite Ba2MgWO6 and Ba2ZnWO6 have been determined using the density functional perturbation theory. The complete set of the zone center vibrational frequencies of these compounds have been determined and classified to different symmetry species. It is found that, the main difference in dielectric constant for Ba2MgWO6 and Ba2ZnWO6 arises from the differences in the mode effective charges of the T1u3 infrared active phonon mode of these compounds. The theoretically obtained dielectric constants are found to be in reasonable agreement with the available experimental data. © 2016 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Dielectric intensities; Double perovskite tungstates; Vibrational frequencies
INDEX KEYWORDS: Calculations; Density functional theory; Dielectric properties; Perovskite; Perturbation techniques; Phonons; Vibrational spectra, Density functional perturbation theory; Double perovskites; Effective charge; First principles; Infrared-active phonon; Phonon calculation, Barium compounds
PUBLISHER: Elsevier B.V.


Vali, R., Khouzestani, H.F. Crossed Andreev reflection in topological insulator F/d-wave SC/F junction (2015) 68, pp. 107-111. Cited 2 times.

DOI: 10.1016/j.physe.2014.12.018

We investigate theoretically the nonlocal conductance arising from the crossed Andreev reflection and electron elastic cotunneling processes in a topological insulator ferromagnet/d-wave superconductor/ferromagnet (F/d-wave SC/F) junction with in-plane magnetization. We find that these nonlocal conductances depend strongly on the d-wave superconducting orientation angular α. The effect of the bias voltage on the crossed Andreev reflection and electron elastic cotunneling is also investigated. Except for α=π/4 case, where crossed Andreev reflection conductance is negligibly small, a perfect crossed Andreev reflection can be obtained in the anti-parallel magnetization configuration by proper tuning of the bias voltage. © 2014 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Andreev reflection; Crossed; Ferromagnet/d-wave superconductor/ferromagnet junction; Topological insulator
INDEX KEYWORDS: Electric insulators; Ferromagnetic materials; Ferromagnetism; Magnetization; Magnets; Superconducting materials, Andreev reflection; Crossed; Crossed Andreev reflections; Elastic cotunneling; Ferromagnets; In-plane magnetization; Magnetization configuration; Topological insulators, Bias voltage
PUBLISHER: Elsevier


Vali, R., Khouzestani, H.F. Coherent conductance and magnetoresistance in a topological insulator ferromagnet/superconductor/ferromagnet junction (2014) 187, pp. 23-27.

DOI: 10.1016/j.ssc.2014.02.004

We investigate theoretically the coherent conductance and magnetoresistance in a topological insulator ferromagnet/superconductor/ferromagnet (F/SC/F) junction with perpendicular magnetization. It is shown that there exists a large difference between the coherent conductance of the parallel and antiparallel magnetization configurations, which leads to a large magnetoresistance. The superconductor layer thickness dependence of the magnetoresistance is discussed in terms of the contributions of the local Andreev reflection, electron elastic cotunneling and crossed Andreev reflection to the parallel and antiparallel conductances. © 2014 Elsevier Ltd.

AUTHOR KEYWORDS: A. Topological insulator; D. Conductance; D. Magnetoresistance
INDEX KEYWORDS: Antiparallel magnetizations; Coherent conductance; Crossed Andreev reflections; Elastic cotunneling; Ferromagnet/superconductor/ferromagnet junction; Perpendicular magnetization; Superconductor layers; Topological insulators, Electric insulators; Magnetization, Magnetoresistance


Vali, R., Khouzestani, H.F. Nonlocal transport properties of topological insulator F/I/SC/I/F junction with perpendicular magnetization (2014) 87 (1), art. no. 25, pp. 1-6. Cited 5 times.
DOI: 10.1140/epjb/e2014-40872-3

We investigate theoretically the nonlocal transport properties in a ferromagnet/insulator/superconductor/insulator/ferromagnet (F/I/SC/I/F) junction with perpendicular magnetization formed on a topological insulator. The nonlocal conductance through the junction depends strongly on whether the perpendicular magnetizations of the two ferromagnets are in a parallel or an antiparallel alignment. This stems from the fact that on the surface of three dimensional topological insulator the exchange field acts as vector potential and from spin-momentum locking property of the topological insulator surface states. It is found that the nonlocal conductance as a function of barrier strength of the I regions exhibits a quantum switch on-off property. © 2014, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

AUTHOR KEYWORDS: Mesoscopic and Nanoscale Systems
INDEX KEYWORDS: Ferromagnetic materials; Ferromagnetism; Locks (fasteners); Magnetization; Magnets; Superconducting materials; Transport properties, Antiparallel alignment; Exchange fields; Mesoscopic and nanoscale systems; Perpendicular magnetization; Quantum switch; Spin momentum; Topological insulators; Vector potential, Electric insulators
PUBLISHER: Springer Heidelberg


Khouzestani, H.F., Vali, R. Nonlocal conductance of topological insulator F/S/I/S/F junction (2014) 21 (6), pp. 2485-2489.

In this work the Non-Local Conductance (NLC) in the topological insulator Ferromagnetic/Superconductor/Insulator/Superconductor/Ferromagnetic (F/S/I/S/F) structure is numerically investigated. The insulator region is a thin barrier and the magnetization of the ferromagnetic regions is considered perpendicular to the surface of the topological insulator. Our results indicate, when the magnetization vectors in the ferromagnetic regions are parallel (anti-parallel), the crossed Andreev reflection (electron elastic cotunneling) process does not occur and also the NLC in terms of barrier strength shows a π periodic behaviour. In addition, the NLC as a function of the barrier strength shows an on-off quantum switching properties. We find also that this junction can be used as a quantum entangler devise which is of high important in quantum computing. © 2014 Sharif University of Technology. All rights reserved.

AUTHOR KEYWORDS: Dirac bogoliubov-de gennes equation; Nonlocal conductance; Topological insulator
INDEX KEYWORDS: Ferromagnetic materials; Ferromagnetism; Magnetization; Quantum computers, Bogoliubov-de Gennes equations; Crossed Andreev reflections; Elastic cotunneling; Ferromagnetic regions; Magnetization vector; Nonlocal; Switching properties; Topological insulators, Electric insulators, quantum mechanics; topology
PUBLISHER: Sharif University of Technology


Vali, R., Vali, M. In-plane magnetoresistance in a topological insulator ferromagnet/barrier/ ferromagnet/superconductor junction (2013) 114 (3), art. no. 033914, . Cited 3 times.

DOI: 10.1063/1.4815881

Dirac Bogoliubov-de Gennes equation and Blonder-Tinkham-Klapwijk formalism are applied to study the conductance and magnetoresistance of a topological insulator ferromagnet/barrier/ferromagnet/superconductor (F1/B/F2/SC) junction with the in-plane magnetization. We find that the induced in-plane magnetization sets a lower critical incident angle for Andreev reflection and causes a very large magnetoresistance. We find also that both the conductance and magnetoresistance are oscillating functions of the gate voltage exerted on the middle ferromagnetic layer and the thickness of this layer. © 2013 AIP Publishing LLC.

INDEX KEYWORDS: Andreev reflection; Bogoliubov-de Gennes equations; Ferromagnetic layers; Ferromagnets; Gate voltages; In-plane magnetization; Lower critical; Topological insulators, Electric insulators; Magnetization, Magnetoresistance


Vali, R., Vali, M. Tunneling conductance and magnetoresistance in topological insulator Fi/I/Fi/d-wave superconductor junctions (2012) 112 (10), art. no. 103919, . Cited 10 times.

DOI: 10.1063/1.4766286

We investigate the tunneling conductance and tunneling magnetoresistance (TMR) in topological insulator ferromagnetic insulator/insulator/ferromagnetic insulator/d-wave superconductor (Fi/I/Fi/d-wave SC) junction, by applying the Blonder-Tinkham-Klapwijk approach. We find that the multiple scatterings in the middle ferromagnetic layer cause the conductance to exhibit an oscillatory behavior as a function of barrier strength even in the case where there is a large Fermi surface mismatch between ferromagnetic and superconductor regions. We find also that the conductance in antiparallel magnetization configuration can be larger than that in the parallel one, depending on the value of barrier strength. This, together with the magnetically induced phase shift of the antiparallel conductance relative to the parallel conductance, leads to a huge negative tunneling magnetoresistance. © 2012 American Institute of Physics.

INDEX KEYWORDS: Antiparallel magnetizations; Ferromagnetic insulator; Ferromagnetic layers; Oscillatory behaviors; Parallel conductance; Superconductor junctions; Topological insulators; Tunneling conductance; Tunneling magnetoresistance, Electric insulators; Ferromagnetic materials; Ferromagnetism; Magnetoresistance; Scanning tunneling microscopy; Superconductivity, Superconducting materials


Vali, R., Vali, M. Conductance properties of topological insulator based ferromagnetic insulator/d-wave superconductor and normal metal/ferromagnetic insulator/d-wave superconductor junctions (2012) 112 (8), art. no. 083911, . Cited 3 times.

DOI: 10.1063/1.4759250

We study theoretically the conductance properties of a ferromagnetic insulator/d-wave superconductor (FI/d-wave SC) junction and a normal metal/ferromagnetic insulator/d-wave superconductor (NM/FI/d-wave SC) junction formed on the surface of a three dimensional topological insulator, where the direction of the magnetization m in ferromagnetic region is perpendicular to the surface. We find that with increasing the magnetization of the ferromagnetic region, a conductance peak to conductance dip conversion occurs, at a bias voltage depending on the d-wave superconducting orientation angular. We find also that the gate voltage applied across the ferromagnetic region strongly affects the influence of the magnetization on the zero bias conductance of the NM/FI/d-wave SC junction. © 2012 American Institute of Physics.

INDEX KEYWORDS: Conductance peaks; Conductance properties; Ferromagnetic insulator; Ferromagnetic regions; Gate voltages; Normal metals; Superconductor junctions; Topological insulators; Zero-bias conductance, Electric insulators; Ferromagnetic materials; Ferromagnetism; Magnetization; Superconducting materials, Superconductivity


Vali, R., Vali, M. Tunneling transport in topological insulator normal metal/insulator/d-wave superconductor junctions (2012) 24 (32), art. no. 325702, . Cited 5 times.

DOI: 10.1088/0953-8984/24/32/325702

We investigate the tunneling conductance in a normal metal/insulator/d-wave superconductor (NM/I/d-wave SC) junction with a barrier of thickness d and with an arbitrary gate voltage V 0 applied across the barrier region, formed on the surface of a topological insulator, using the Dirac-Bogoliubov-de Gennes equation and Blonder-Tinkham-Klapwijk(BTK) formalism. We find that the tunneling conductance as a function of both d and V 0 displays an oscillatory behavior whose amplitude decreases with increase of V 0. We also find that when the Andreev resonant condition is met, the tunneling conductance approaches a maximum value of 2G 0, independent of the gate voltage V 0. © 2012 IOP Publishing Ltd.

INDEX KEYWORDS: Gate voltages; Maximum values; Normal metals; Oscillatory behaviors; Resonant condition; Superconductor junctions; Topological insulators; Tunneling conductance, Electric insulators; Resonant tunneling; Superconducting materials; Superconductivity, Scanning tunneling microscopy


Vali, R. Electronic properties and phonon spectra of SrMoO4 (2011) 50 (9), pp. 2683-2687. Cited 15 times.

DOI: 10.1016/j.commatsci.2011.04.018

The electronic band structure, dielectric function, and phonon spectra of SrMoO4 have been studied using density functional theory within the local density approximation. The origin of the peaks in the imaginary part of the dielectric function was analyzed based on the electronic structure. The calculated phonon spectra are in good agreement with available Raman experimental data and provide benchmark theoretical results for the interpretation of future infrared phonon measurements. © 2011 Elsevier B.V. All rights reserved.

INDEX KEYWORDS: Dielectric functions; Electronic band structure; Experimental data; Imaginary parts; Phonon spectrum; Theoretical result, Electronic properties; Electronic structure; Local density approximation, Phonons


Vali, R. Infrared and Raman spectra and the band structure of yttrium trifluoride YF3 (2011) 50 (8), pp. 2391-2396. Cited 6 times.

DOI: 10.1016/j.commatsci.2011.03.017

The infrared and nonresonant Raman spectra of YF3 have been studied within the framework of density functional perturbation theory. We report the calculated frequencies of three Raman active modes and one IR active mode that could not be detected experimentally. The valence and conduction band structure of YF3 have been calculated, using density functional theory. A good agreement between the calculated valence band width and experimental result was obtained, and an indirect energy gap of 7.58 eV is estimated in the local density approximation. © 2011 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Electronic band structure; Infrared reflectivity; Raman intensity; YF3
INDEX KEYWORDS: Active mode; Density functional perturbation theory; Electronic band structure; Infrared and Raman spectra; Infrared reflectivity; Nonresonant; Raman active modes; Raman intensity; Raman spectra; YF3; Yttrium trifluoride, Band structure; Electron mobility; Perturbation techniques; Raman scattering; Raman spectroscopy; Reflection; Yttrium, Density functional theory


Vali, R., Salehi, S. Spin conductance and spin filtering in ferromagnetic semiconductor quantum point contacts (2010) 150 (47-48), pp. 2306-2309.

DOI: 10.1016/j.ssc.2010.10.012

By combining the spin dependent transport properties of the ferromagnetic semiconductors with the basic physics of the quantum point contacts, we investigate the spin polarized transport through ferromagnetic semiconductor quantum point contacts. We find that the spin conductance strongly depends on the spin orientation, the magnitude of the spin splitting energy and the shape of the cross sections of the point contacts. © 2010 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: A. Ferromagnetic semiconductors; A. Quantum point contacts; D. Spin filtering
INDEX KEYWORDS: Cross section; D. Spin filtering; Ferromagnetic semiconductor; Quantum point contact; Spin filtering; Spin orientations; Spin polarized transport; Spin splittings; Spin-dependent transport properties, Ferromagnetic materials; Ferromagnetism; Point contacts; Spin polarization; Transport properties, Quantum chemistry


Vali, R., Mirzanian, S.M. Effect of Rashba spin-orbit coupling on the spin polarized transport in diluted magnetic semiconductor barrier structures (2009) 149 (45-46), pp. 2032-2035. Cited 7 times.

DOI: 10.1016/j.ssc.2009.08.027

We investigate theoretically the effects of Rashba spin-orbit coupling on the spin dependent transport through diluted magnetic semiconductor single and double barrier structures in the presence of a magnetic field. We find that the Rashba spin-orbit coupling gives rise to an enhancement of the negative tunnelling magnetoresistance of the diluted magnetic semiconductor single barrier structure and a pronounced beating pattern in the tunnelling magnetoresistance and spin polarization of the diluted magnetic semiconductor double barrier structure. © 2009 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: A. Diluted magnetic semiconductor; D. Rashba spin-orbit coupling; D. Tunnelling magnetoresistance
INDEX KEYWORDS: A. Diluted magnetic semiconductor; Barrier structures; D. Rashba spin-orbit coupling; D. Tunnelling magnetoresistance; Diluted magnetic semiconductors; Double-barrier structures; Rashba spin-orbit coupling; Spin dependent transport; Spin polarized transport; Tunnelling magnetoresistance, Electric resistance; Magnetic semiconductors; Magnetism; Magnetoelectronics; Magnetoresistance; Orbits; Semiconductor quantum wires; Spin dynamics; Spin polarization; Tunneling (excavation); Wind tunnels, Magnetic field effects


Vali, R. Ab initio vibrational and dielectric properties of Y V O4 (2009) 149 (39-40), pp. 1637-1640. Cited 7 times.

DOI: 10.1016/j.ssc.2009.06.036

For the yttrium orthovanadate Y V O4 with a tetragonal zircon-type structure, the first complete set of Raman-active and IR-active phonon modes has been calculated using ab initio density functional perturbation theory. The calculated IR reflectivity spectra are in good agreement with available experimental data. We report the calculated frequencies of three Raman-active modes that could not be detected experimentally and a new assignment of the experimental Raman data. The contributions of each IR-active phonon modes to static dielectric tensor have been determined. © 2009 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: A. Y V O4; D. IR reflectivity spectra; D. Phonons
INDEX KEYWORDS: A. Y V O4; Ab initio; D. IR reflectivity spectra; D. Phonons; Density functional perturbation theory; Dielectric tensors; Experimental data; IR reflectivity; Phonon mode; Raman active modes; Raman data; Yttrium orthovanadate; Zircon-type structures, Density functional theory; Dielectric properties; Perturbation techniques; Reflection; Silicate minerals; Yttrium; Zircon, Phonons


Vali, R. Lattice dynamics of room temperature orthorhombic SrHfO3 (2009) 149 (13-14), pp. 519-522. Cited 17 times.

DOI: 10.1016/j.ssc.2009.01.012

The lattice dynamics of room temperature orthorhombic phase of SrHfO3 has been computed, using density functional perturbation theory. The full set of zone center phonon frequencies and infrared reflectivity spectra were reported, providing benchmark theoretical results for the interpretation of future experimental phonon measurements. It is found that the static dielectric constant is relatively anisotropic. This anisotropy has been discussed in relationship to the oscillator strengths and contributions of the lowest IR active modes. © 2009 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: A. SrHfO3; D. IR reflectivity spectra; D. Lattice dynamics; D. Phonon modes
INDEX KEYWORDS: Anisotropy; Crystal lattices; Density functional theory; Infrared spectroscopy; Lattice vibrations; Perturbation techniques; Phonons; Programming theory; Reflection; Solids, A. SrHfO3; D. IR reflectivity spectra; D. Lattice dynamics; D. Phonon modes; Density functional perturbation theories; Dielectric constants; Infrared reflectivity spectrum; Orthorhombic phase; Oscillator strengths; Room temperatures; Theoretical results; Zone-center phonons, Dynamics


Vali, R. Phonons and heat capacity of LaAlO3 (2008) 44 (2), pp. 779-782. Cited 11 times.

DOI: 10.1016/j.commatsci.2008.05.029

The ab initio calculations of the phonon dispersion relations for cubic and rhombohedral phases of LaAlO3 were performed using the density functional perturbation theory together with plane-wave expansion and norm conserving pseudopotentials. In the cubic phase the phonon dispersion curves show a soft mode at the R-point. This soft mode leads to the observed cubic-rhombohedral phase transition. The phonon dispersion relations of rhombohedral LaAlO3 confirm the dynamical stability of this phase. The calculated heat capacity of rhombohedral LaAlO3 is in very good agreement with available experimental result. © 2008 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Ab initio calculations; Heat capacity; LaAlO3; Phase transitions; Phonon dispersion relations; Phonons
INDEX KEYWORDS: Acoustic dispersion; Density functional theory; Dispersion (waves); Lanthanum alloys; Perturbation techniques; Phase stability; Phonons; Quantum theory; Specific heat; Stability; Strain measurement, Ab initio calculations; Density functional perturbation theories; Dynamical stabilities; Heat capacities; Heat capacity; LaAlO3; Phonon dispersion curves; Phonon dispersion relations; Phonon dispersions; Pseudo potentials; Rhombohedral phase; Rhombohedral phases; Soft modes; Wave expansions, Phase transitions


Vali, R. Structural phases of SrHfO3 (2008) 148 (1-2), pp. 29-31. Cited 28 times.

DOI: 10.1016/j.ssc.2008.07.018

Structural optimizations were performed for all previously predicted phases of SrHfO3, using density functional theory. The phonon dispersion relations of cubic P m over(3, -) m phase of SrHfO3 have been calculated within density functional perturbation theory. Instabilities have been observed along the M - Γ - R - M line in the Brillouin zone. Based on the soft mode frequencies and calculated ground state energies we conclude that the I m m a, I 4 / m c m and P b n m phases are likely to exist, while P 4 m m and C m c m phases are not likely to occur. © 2008 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: C. Crystal structure; D. Phase transitions; D. Phonons
INDEX KEYWORDS: Structural design, C. Crystal structure; D. Phase transitions; D. Phonons; Structural phases, Structural optimization


Vali, R., Sadrollahi, E. Spin-dependent transmission of holes through a semiconductor quantum wire with multiple stub (2008) 40 (10), pp. 3155-3159. Cited 1 time.

DOI: 10.1016/j.physe.2008.05.005

The spin transport of holes through a quantum wire made of many identical T-shaped diluted magnetic semiconductor/semiconductor units is investigated theoretically. The spin-down and spin-up transmission coefficients have been studied as a function of stub parameters. The spin-up transmission coefficient as a function of the stub length is extremely negligible, in the case of multiple-stub quantum wire, while the spin-down transmission coefficient shows a nearly periodic behaviour with regions of large transmission separated by forbidden bands. The spin polarization switches periodically between one and zero as the stub length is changed and shows a square-wave pattern. © 2008 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Multiple stub; Quantum wire; Spin transport
INDEX KEYWORDS: Nanostructures; Nanowires; Quantum chemistry; Quantum electronics; Semiconductor quantum dots; Semiconductor quantum wires; Wire, Forbidden bands; Multiple stub; Quantum wire; Quantum wires; Spin polarizations; Spin transport; Spin transports; Spin-dependent transmission; Spin-down; Spin-up; Square waves; T-shaped; Transmission coefficients, Spin dynamics


Vali, R. Lattice dynamics and electronic properties of the scintillator host material: Barium hafnate (2008) 147 (1-2), pp. 1-3. Cited 20 times.

DOI: 10.1016/j.ssc.2008.04.035

The electronic properties of barium hafnate were studied using the density functional theory. It is found that barium hafnate is an indirect band gap insulator. The phonon frequencies and dielectric constants have been calculated, using density functional perturbation theory. Based on the calculated physical values and by following the Lempicki and Wojtowicz formulation we evaluated the saturation value of the light output for barium hafnate, which is in good agreement with the experimental value. © 2008 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: D. Electronic band structure; D. Light output; D. Phonons
INDEX KEYWORDS: Barium compounds; Density functional theory; Electronic properties; Lattice vibrations, Barium hafnate; Host materials, Phosphors


Vali, R. Lattice dynamics of cubic SrZrO3 (2008) 69 (4), pp. 876-879. Cited 17 times.

DOI: 10.1016/j.jpcs.2007.09.022

Using density functional perturbation theory, the optical dielectric constant, Born effective charges and phonon dispersion curves of cubic SrZrO3 have been calculated. The obtained dispersion curves show a soft phonon branch spreading from R to M points of the cubic Brillouin zone. An analysis based on the symmetry relationships indicates that the experimentally observed low-symmetry phases of SrZrO3 can be considered as results of the soft mode condensation at R and M points. © 2007 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: A. Oxides; C. Ab initio calculations; D. Lattice dynamics; D. Phonons
INDEX KEYWORDS: Brillouin scattering; Crystal symmetry; Density functional theory; Lattice vibrations; Permittivity; Perturbation techniques; Phonon scattering, Ab initio calculations; Cubic Brillouin; Optical dielectric constants; Phonon dispersions, Strontium compounds


Vali, R. Band structure and dielectric properties of orthorhombic SrZrO3 (2008) 145 (9-10), pp. 497-501. Cited 22 times.

DOI: 10.1016/j.ssc.2007.12.009

Ab initio density functional theory has been used to study the electronic band structure, k = 0 (zone center) vibrational modes, and dielectric properties of the crystalline high-κ perovskite oxide SrZrO3. The frequencies of the k = 0 normal modes are computed by the linear response technique and then grouped according to their symmetry. The dielectric intensity of each IR-active mode has been determined. It is found that the calculated orientationally averaged static dielectric constant ε0 = 21.49 is in good agreement with experiment. © 2007 Elsevier Ltd. All rights reserved.

AUTHOR KEYWORDS: A. SrZrO3; D. Band structure; D. Dielectric constant; D. Phonon modes
INDEX KEYWORDS: Density functional theory; Permittivity; Perovskite; Phonons; Strontium compounds; Vibration analysis, Electronic band structure; Phonon modes; Vibrational modes, Band structure


Vali, R. Spin filtering through Cd1-yMgyTe/Cd1-xMnxTe heterostructure (2008) 40 (3), pp. 637-642. Cited 2 times.

DOI: 10.1016/j.physe.2007.08.076

The spin filtering through Cd1-yMgyTe/Cd1-xMnxTe heterostructure, both with zero and with positive zero-field conduction band offset, is investigated theoretically. The magnetic field dependence of the transmission coefficients, current densities, and spin polarizations for considered systems have been studied. It is found that a positive zero-field conduction band offset as high as 3 meV shifts considerably the onset of the spin-up complete suppression to lower magnetic field region and thereby unity spin polarization initiates at lower magnetic field. © 2007 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Cd1-yMgyTe/Cd1-xMnxTe heterostructure; Diluted magnetic semiconductors; Spin filtering
INDEX KEYWORDS: Cadmium; Conduction bands; Current density; Magnetic field effects; Magnetic semiconductors; Spin polarization, Diluted magnetic semiconductors; Spin filtering; Transmission coefficients, Heterojunctions


Vali, R. Vibrational, dielectric and scintillation properties of YAlO3 (2007) 127 (2), pp. 727-730. Cited 9 times.

DOI: 10.1016/j.jlumin.2007.04.009

Vibrational and dielectric properties of YAlO3 are investigated within the framework of density functional perturbation theory. The calculated zone center phonon frequencies and dielectric constants are in good agreement with available experimental data. Based on the theoretical values of the dielectric constants and the highest longitudinal IR phonon energy and using the phenomenological model of Lempicki and Wojtowicz, we investigate the scintillation properties of the YAlO3. © 2007 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Dielectric permittivity; Phonon modes; Scintillation; YAlO3
INDEX KEYWORDS: Density functional theory; Mathematical models; Permittivity; Perturbation techniques; Scintillation, Density functional perturbation theory; Dielectric permittivity; Phonon frequencies; Phonon modes, Yttrium compounds


Vali, R. Electronic, dynamical, and dielectric properties of lanthanum oxysulfide (2006) 37 (3), pp. 300-305. Cited 15 times.

DOI: 10.1016/j.commatsci.2005.08.007

The electronic band structure, lattice dynamics and dielectric properties of lanthanum oxysulfide (La2O2S) have been investigated within density functional theory. It is found that lanthanum oxysulfide is an indirect band-gap semiconductor. Density functional perturbation theory is employed to evaluate the phonon frequencies at the center of the Brillouin zone, the Born effective charge tensors, and the dielectric permittivity tensors. The results of a band-by-band decomposition of the Born effective charges are given and the origin of the anomalous Born effective charges and the character of the bonding are discussed. The present calculation predicts the frequencies of two IR-active modes that were not observed in experiment. © 2005 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: Born effective charge; Density-functional theory; Dielectric permittivity; Electronic band structure; La2O2S; Phonon modes
INDEX KEYWORDS: Band structure; Dielectric properties; Electronic structure; Permittivity; Perturbation techniques; Probability density function, Born effective charge; Dielectric permittivity; Electronic band structure; La2O2S; Phonon modes, Lanthanum compounds


Vali, R., Hosseini, S.M. First-principles study of structural, dynamical, and dielectric properties of A-La2O3 (2004) 31 (1-2), pp. 125-130. Cited 20 times.

DOI: 10.1016/j.commatsci.2004.02.003

We have investigated the structural, dynamical, and dielectric properties of A-La2O3, within density-functional theory. The relaxed structural parameters are found to be in very good agreement with experimental data. Density-functional perturbation theory was used to calculate the zone-center phonon frequencies, Born effective charge tensors, and the dielectric permittivity tensors. The static permittivity constant is decomposed to its electronic component and the individual contribution of IR-active modes. It is found, for both the direction parallel to the trigonal axis and the direction perpendicular to it, that the ionic contribution to the static dielectric permittivity is mostly due to a single IR-active mode. © 2004 Elsevier B.V. All rights reserved.

AUTHOR KEYWORDS: A-La2O3; Density-functional theory; Dielectric permittivity tensors; Gate-dielectric
INDEX KEYWORDS: Crystal structure; Decomposition; Electron gas; Fourier transforms; Ions; Parameter estimation; Permittivity; Phonons; Probability density function; Reaction kinetics; Thermodynamic stability, Dielectric permittivity tensors; Gate-dielectrics; Structural parameters; Structural relaxation, Materials science


Vali, R., Hosseini, S.M. First-principles study of structural, dynamical, and dielectric properties of κ-Al2O3 (2004) 29 (2), pp. 138-144. Cited 12 times.

DOI: 10.1016/j.commatsci.2003.06.009

We have performed a first-principles study of the structural, dynamical, and dielectric properties of κ-Al2O3. The relaxed structural parameters are found to be in excellent agreement with experimental data. Using density-functional perturbation theory, we obtain the Born effective charge tensors, the phonon frequencies at the center of the Brillouin zone, and the electronic and static dielectric permittivity tensors of κ-Al2O3. Using our calculated results of κ-Al2O3, together with the previous theoretical results of α-Al2O3 and available experimental data of amorphous Al2O3, we demonstrate the coordination dependence of ionic contribution to static dielectric constant of Al 2O3. © 2003 Published by Elsevier B.V.

AUTHOR KEYWORDS: κ-Al2O3; Density-functional theory; Dielectric permittivity tensors; Gate-dielectric
INDEX KEYWORDS: Amorphous alloys; Brillouin scattering; Crystal structure; Dielectric properties; Ionic conduction; Tensors, Density functional theory (DFT); Dielectric permittivity tensors, Alumina

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