Loading...
Search for:
first-principles
0.007 seconds
Total 52 records
The Effect of Pressure on the Coexistence of Superconductivity and Magnetism in RuSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2O10-δ
, Ph.D. Dissertation Sharif University of Technology ; Akhavan, Mohammad (Supervisor)
Abstract
The coexistence of long-range magnetic order and superconductivity in the ruthenocuprate families, Ru1212 and Ru1222 has been studied both theoretically and experimentally. Historically these two different phases are incompatible with each other and in the most previous research reported on the coexistence of these phases, there have been observed separated magnetic and superconducting phases. However in the ruthenocuprate families, there is a single phase with both magnetic and superconducting phase which coexist with each other. It has been determined that superconductivity arises in CuO2 planes, and magnetic orders occur in RuO2. From experimental point of view, we have investigated the...
First Principles Studies of Mechanical, Physical, and Electronic Properties of a-Si - also, Diffusion of a Self-interstitial Atom in an Ultra-thin fcc Film Via Lattice Statics
, Ph.D. Dissertation Sharif University of Technology ; Mohammadi Shodja, Hossein (Supervisor)
Abstract
By employing first principles density functional theory-based (DFT) molecular dynamics (MD), the influences of dangling and floating bonds as well as distorted tetrahedral bonds are studied on the mechanical, physical, and electronic properties of amorphous Si (a-Si). For further examination of the effects of these geometrical defects, two distinct amorphous samples, namely as-quenched and annealed are generated and examined. To verify the validity of the representative cells, the obtained radial distribution function, pair correlation function, and cohesive energy are compared with those corresponding results presented in the literature. Moreover, the surface energy is calculated at final...
First-principle electronic structure calculation of BaFe2-x Cox As2 (X = 0,1, 2) superconductor
,
Article
Journal of Superconductivity and Novel Magnetism
;
Volume 28, Issue 8
,
August
,
2015
,
Pages 2249-2254
;
15571939 (ISSN)
; Khosroabadi, H
; Akhavan, M
;
Sharif University of Technology
Springer New York LLC
2015
Abstract
The equilibrium crystal structure and electronic structure of BaFe2-x Cox As2 (x = 0,1, 2) superconductor have been investigated by using the pseudopotential Quantum Espresso code based on the ab initio density functional theory in the generalized gradient approximation. The equilibrium crystal structure for x = 1.0 has been determined by considering five different Fe/Co configurations. This study shows that the spin calculation is essential to obtain the experimental values at x = 0.0. The total and partial density of states, band structure, and Fermi surfaces of the three compounds has been calculated. Density of states calculation indicates the important...
Effects of fluorine doping and pressure on the electronic structure of lao1−x fx feas superconductor: a first principle study
, Article Journal of Superconductivity and Novel Magnetism ; Volume 30, Issue 8 , 2017 , Pages 2065-2071 ; 15571939 (ISSN) ; Khosroabadi, H ; Sharif University of Technology
Springer New York LLC
2017
Abstract
The effects of fluorine doping on the electronic structure of LaO1−xFxFeAs superconductor have been investigated by ab initio density functional theory using pseudopotential quantum espresso code. Firstly, we have studied the role of fluorine doping on the electronic structure of LaO1−xFxFeAs by calculation of band structure, density of states, and Fermi surfaces at various doping levels x = 0.00, 0.25, and 0.50. The lattice parameters and ionic position have been determined by optimizing crystal structure. Our results show that doping decreases cell volume similar to mechanical pressure and shifts the bands and states near the Fermi level toward the lower energies. According to the Fermi...
First-principles study of molecule adsorption on Ni-decorated monolayer MoS2
, Article Journal of Computational Electronics ; Volume 18, Issue 3 , 2019 , Pages 826-835 ; 15698025 (ISSN) ; Berahman, M ; Asgari, R ; Sharif University of Technology
Springer New York LLC
2019
Abstract
The interactions between four different gas molecules (methanol, o-xylene, p-xylene and m-xylene) and Ni-decorated monolayer MoS2 were investigated by means of density functional computations to exploit its potential application as a gas sensor. The electronic properties of the Ni-decorated monolayer MoS2 and gas molecule (adsorbent–adsorbate properties) strongly depend on the Ni-decorated monolayer MoS2 structure and the molecular configuration of the adsorbate. The adsorption properties of volatile organic compound (VOC) molecules on Ni-decorated MoS2 has been studied taking into account the parameters such as adsorption energy, energy bandgap, density of states, and Mulliken charge...
The importance of electron correlation in graphene and hydrogenated graphene
, Article European Physical Journal B ; Volume 88, Issue 10 , October , 2015 ; 14346028 (ISSN) ; Jafari, S. A ; Sharif University of Technology
springer berlin
2015
Abstract
Local density approximation (LDA) and Green function effective Coulomb (GW) calculations are performed to investigate the effect of electronic correlations on the electronic properties of both graphene and graphane. The size of band gap in graphane increases from 3.7 eV in LDA to 4.9 eV in GW approximation. By calculating maximally localized Wannier wave functions, we evaluate the necessary integrals to get the Hubbard U and the exchange J interaction from first principles for both graphene and graphane. Our ab-initio estimates indicate that in the case of graphene, in addition to the hopping amplitude t ∼ 2.8 eV giving rise to the Dirac nature of low lying excitations, the Hubbard U value...
Near-room-temperature spin caloritronics in a magnetized and defective zigzag MoS2 nanoribbon
, Article Journal of Computational Electronics ; Volume 19, Issue 1 , 2020 , Pages 137-146 ; Fathipour, M ; Faez, R ; Darvish, G ; Sharif University of Technology
Springer
2020
Abstract
Using a tight-binding approach and first-principles calculations combined with the nonequilibrium Green’s function method, the thermal spin transport in a zigzag molybdenum disulfide (MoS 2) nanoribbon in the proximity of a ferromagnetic insulator that induces a local exchange magnetic field in the center of the nanoribbon is investigated. It is found that a pure spin current and perfect spin Seebeck effect with zero charge current can be generated by applying a thermal gradient and local exchange magnetic field without a bias voltage near room temperature. Furthermore, it is shown that this nanoscale device can act as a spin Seebeck diode for the control of thermal and spin information in...
Wardrop's first principle: Extension for capacitated networks
, Article Scientia Iranica ; Volume 28, Issue 1 , 2021 , Pages 175-191 ; 10263098 (ISSN) ; Poorzahedy, H ; Nourinejad, M ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
In transportation literature, User Equilibrium (UE) has been widely studied since early 1950's, many studies of which define equilibrium flow of traffic for uncapacitated networks based on Wardrop's first principle, implying also a Nash Equilibrium (NE). Although, in general, the two equilibria (UE and NE) are not explicitly the same, they are shown to be equivalent under special conditions for uncapacitated UE, when volume delay functions are separable, continuous, non-decreasing and non-negative. A good deal of research is devoted to explain UE in capacitated networks based on Wardrop's first principle and the concept of generalized costs. However, UE for capacitated networks, even under...
Wardrop's first principle: Extension for capacitated networks
, Article Scientia Iranica ; Volume 28, Issue 1 , 2021 , Pages 175-191 ; 10263098 (ISSN) ; Poorzahedy, H ; Nourinejad, M ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
In transportation literature, User Equilibrium (UE) has been widely studied since early 1950's, many studies of which define equilibrium flow of traffic for uncapacitated networks based on Wardrop's first principle, implying also a Nash Equilibrium (NE). Although, in general, the two equilibria (UE and NE) are not explicitly the same, they are shown to be equivalent under special conditions for uncapacitated UE, when volume delay functions are separable, continuous, non-decreasing and non-negative. A good deal of research is devoted to explain UE in capacitated networks based on Wardrop's first principle and the concept of generalized costs. However, UE for capacitated networks, even under...
Monoelemental two-dimensional iodinene nanosheets: A first-principles study of the electronic and optical properties
, Article Journal of Physics D: Applied Physics ; Volume 55, Issue 13 , 2022 ; 00223727 (ISSN) ; Stampfl, C ; Faraji, M ; Mortazavi, B ; Fadlallah, M. M ; Nguyen, C. V ; Fazeli, S ; Ghergherehchi, M ; Sharif University of Technology
IOP Publishing Ltd
2022
Abstract
Very recently, two-dimensional (2D) iodinene, a novel layered and buckled structure has been successfully fabricated (Qian et al 2020 Adv. Mater. 32 2004835). Motivated by this latest experimental accomplishment, for the first time we conduct density functional theory, first-principles calculations to explore the structural, electronic, and optical properties of monolayer, few-layer and bulk iodinene. Unlike the majority of monoelemental 2D lattices, iodinene is predicted to be an intrinsic semiconductor. On the basis of calculations using the generalized gradient approximation of Perdew-Burke-Ernzerhof for the exchange-correlation functional and the Heyd-Scuseria-Ernzerhof (HSE06)...
Manipulation of structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet through vacancy defects: First-principles numerical simulations based on density-functional-theory along with tight-binding approximation
, Article Materials Research Express ; Volume 6, Issue 8 , 2019 ; 20531591 (ISSN) ; Irfan, M ; Iqbal, A ; Shahid, F. A ; Junaid Amjad, R ; Usman, A ; Mahmood, H ; Latif, H ; Imran, M ; Akhtar Ehsan, S ; Akhtar, M. N ; Akbar, N ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
Using the first-principles procedure of density-functional-theory within tight-binding approximation and nonequilibrium Green's function formalism, this paper reports on the impact of vacancy defects on the structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet. After the introduction of vacancy defects in graphene atomic sheet passivated with hydrogen atoms, apart from increase in band gap, a suppression is noted in the intensity of transmission channels and density of states arising from the long array deformations of the graphene sheet and a corresponding shift of the Fermi level. This in turn decreases the conductance of the defected graphene atomic...
First-principles study on ZnV2O6 and Zn2V2O7: two new photoanode candidates for photoelectrochemical water oxidation
, Article Ceramics International ; Volume 44, Issue 6 , 2018 , Pages 6607-6613 ; 02728842 (ISSN) ; Sabbagh Alvani, A. A ; Naseri, N ; Du, S ; Rosei, F ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
We used first principles calculations based on density functional theory with generalized gradient approximation to investigate and compare the structural, electronic and optical properties of two photoanode materials, ZnV2O6 and Zn2V2O7, for use in photocatalytic water splitting. After geometry optimization, the calculated structural parameters evince a satisfactory agreement with the reported experimental results indicating that the used method and conditions are suitable. The electronic structures demonstrate that both photocatalysts possess favorable band gaps (2.31 and 2.52 eV) and appropriate band edge positions for oxygen evolution reaction under solar radiation. The relatively light...
Optimal-time quadcopter descent trajectories avoiding the vortex ring and autorotation states
, Article Mechatronics ; Volume 68 , 2020 ; Antunes, D ; Nejat Pishkenari, H ; Alasty, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
It is well-known that helicopters descending fast may enter the so-called Vortex Ring State (VRS), a region in the velocity space where the blade's lift differs significantly from regular regions and high amplitude fluctuations are often present. These fluctuations may lead to instability and, therefore, this region is avoided, typically by increasing the horizontal speed. This paper researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel experiments. Moreover, we propose that the so-called Windmill-Brake State (WBS) or autorotation region should also be avoided for...
Enhanced ORR catalytic activity of rare earth-doped Gd oxide ions in a CoFe2O4 cathode for low-temperature solid oxide fuel cells (LT-SOFCs)
, Article Ceramics International ; Volume 48, Issue 19 , 2022 , Pages 28142-28153 ; 02728842 (ISSN) ; Akbar, M ; Yousaf Shah, M. A. K ; Noor, A ; Lu, Y ; Akhtar, M. N ; Mushtaq, N ; Hu, E ; Yan, S ; Zhu, B ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
The search for cathode materials with fast oxygen reduction reaction (ORR) catalytic activities and high ionic conductivity is the key obstacle to SOFCs commercialization and its operation at low temperatures. In order to search for a cathode with enhanced catalytic functionality, herein we report a single-phase CoFe2O4 (CFO) and CoGd0.2Fe1.80O4 (CGFO), which can be employed as an active cathode to improve electrocatalytic ORR functionalities at low temperature. It is found that CGFO having enriched oxygen vacancies exhibits the least polarization resistance (RP) of 0.42 Ωcm2 compared to the pure CFO which shows polarization resistance of 0.56 Ω cm2 under H2/air conditions. Furthermore,...
Elastic moduli tensors, ideal strength, and morphology of stanene based on an enhanced continuum model and first principles
, Article Mechanics of Materials ; Volume 110 , 2017 , Pages 1-15 ; 01676636 (ISSN) ; Ojaghnezhad, F ; Etehadieh, A ; Tabatabaei, M ; Sharif University of Technology
Elsevier B.V
2017
Abstract
The present work aims to provide an accurate description of the tensile behavior of the planar as well as low-buckled stanene and to capture their ideal strength in armchair (AC)- and zigzag (ZZ)-directions. For an accurate description of anisotropic response of such hyperelastic materials as stanene, consideration of a highly nonlinear constitutive model in which up to the fourth power of strains is incorporated is inevitable. By utilizing first principles calculations based on density functional theory (DFT), the second, third, fourth, and fifth order elastic moduli tensors corresponding to both planar and low-buckled states are obtained. Moreover, the morphology of the free-standing...
Thermally induced spin-dependent current based on Zigzag Germanene Nanoribbons
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 86 , 2017 , Pages 175-183 ; 13869477 (ISSN) ; Faez, R ; Sharif University of Technology
Elsevier B.V
2017
Abstract
In this paper, using first principle calculation and non-equilibrium Green's function, the thermally induced spin current in Hydrogen terminated Zigzag-edge Germanene Nanoribbon (ZGeNR-H) is investigated. In this model, because of the difference between the source and the drain temperature of ZGeNR device, the spin up and spin down currents flow in the opposite direction with two different threshold temperatures (Tth). Hence, a pure spin polarized current which belongs to spin down is obtained. It is shown that, for temperatures above the threshold temperature spin down current increases with the increasing temperature up to 75 K and then decreases. But spin up current rises steadily and in...
Pressure dependence of effective Coulomb interaction parameters in BaFe2As2 by first-principle calculation
, Article Physica C: Superconductivity and its Applications ; Volume 548 , 15 May , 2018 , Pages 61-64 ; 09214534 (ISSN) ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Pressure dependence of the onsite Coulomb interactions of the BaFe2As2 has been studied by employing the constrained random phase approximation within first-principle calculations. Analyzing total and projected density of states, a pseudogap is found for dxy band at the energy roughly 0.25 eV higher than the Fermi level. Also, by applying pressure the spectral weight of the dxy orbital vanishes while other orbitals remain metallic. The different screening channels, as discussed in four different models, affect significantly on the Hubbard U while the Hund J remains almost unchanged. The average onsite bare and partially and fully screened Coulomb interactions increase with different rates...
Pressure effect on the mechanical and electronic properties of B3N3: a first-principle study
, Article Physica C: Superconductivity and its Applications ; Volume 548 , 15 May , 2018 , Pages 50-54 ; 09214534 (ISSN) ; Faez, R ; Sharif University of Technology
Elsevier B.V
2018
Abstract
In this paper, we perform Self-Consistent Field (SCF) energy calculation of Tetragonal B3N3 in the homogenous pressure range of −30 GPa to +160 GPa. Also, we study mechanical and electronic properties of this compound as a potential candidate for a conventional phonon-mediated superconductor with a high transition temperature. To do this, the volume changes of B3N3, and its bulk modulus, due to applying pressure in the range of −30 GPa to +160 GPa are calculated and analyzed. The calculated Bulk modulus of B3N3 at 230 GPa in the relaxed condition indicates the strength of bonds and its low compressibility. We calculated and analyzed the electronic effective mass in both XM and MA directions...
Mechanical and chemical pressure effects on the AeFe 2 As 2 (Ae = Ba, Sr, Ca) compounds: Density functional theory
, Article Computational Materials Science ; Volume 160 , 2019 , Pages 233-244 ; 09270256 (ISSN) ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
Elsevier B.V
2019
Abstract
We have studied the pressure-induced structural, magnetic and electronic properties of AeFe 2 As 2 (Ae = Ba, Sr, Ca) compounds in the framework of density functional theory within the GGA-PBE method. The effects of chemical pressure generated by Sr and Ca substitutions in BaFe 2 As 2 have been investigated. We have found a magnetic transition at the same primitive unit cell volume, around 81 Å 3 for the (Ba⧹Ca)Fe 2 As 2 compounds, which predicts a magnetic transition pressure of 12 GPa for SrFe 2 As 2 . The structural parameters of FeAs 4 tetrahedra are obtained after ionic relaxation and compared with the existing experimental results. The change of these internal parameters is ascribed to...
Computational study of spin caloritronics in a pristine and defective antimonene nanoribbon
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 120 , 2020 ; Faez, R ; Darvish, G ; Sharif University of Technology
Elsevier B.V
2020
Abstract
In this paper, by using first-principle density functional theory (DFT) combined with non-equilibrium Green's function (NEGF), thermally induced spin current in zigzag and armchair Antimonene Nanoribbon (SbNR) is investigated. Also, we obtain higher spin current in Armchair nanoribbon (ANR) than zigzag nanoribbon (ZNR), because the start energy of transmission for ANR is closer to the Fermi level than ZNR. The results show that the device has a perfect spin Seebeck effect under temperature difference without gate voltage or bias voltage. For the ANR configuration, the competition between spin up holes and spin down electrons leads to negative differential behavior of charge current, which is...