Aminollah Vaez | University of Isfahan (original) (raw)

Papers by Aminollah Vaez

Physica E-low-dimensional Systems & Nanostructures, Sep 1, 2018

In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNi... more In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNiX (X= Ga and In) half-Heusler compounds have been studied. The calculations have been done based on the density functional theory in the framework of the Wien2k package. The generalized gradient approximation was used for the exchange-correlation functional. Electronic structures and density of states of the bulks and NLs of the compounds show that, they are nonmagnetic and metal. It is found that, the bulks of compounds don't have topological phase, but the NLs of compounds have topological phase. Thus, the NLs of both compounds are topological metals. Important optical properties of these compounds were acquired. The results show that, there is optical anisotropy in the NLs, between the in-plane (x) and out-of-plane (z) directions. The absorptions of the bulks and NLs of the compounds are high in the UV range.

Chinese Physics B, Dec 1, 2013

ABSTRACT

Chemical Physics Letters, Apr 1, 2007

Molecular dynamics (MD) simulation is used to compute the adsorption isotherms of xenon (Xe) gas ... more Molecular dynamics (MD) simulation is used to compute the adsorption isotherms of xenon (Xe) gas on defected open ended singlewalled nanotubes (o-SWNT). We perform a simulation based on a many-body interatomic Brenner potential with a two-body interatomic Lennard-Jones (LJ) potential. Adsorption isotherms of Xe on (10, 10) o-SWNT for several temperatures, between 95 and 130 K, are measured. Adsorption coverage, isosteric heat, and binding energy were calculated at various temperatures and pressures and compared with the same properties for the perfect (10, 10) o-SWNT. It is shown that adsorption occurs both inside and outside of an o-SWNTs.

Journal of Superconductivity and Novel Magnetism, Dec 20, 2012

The magnetic properties of Mn x Fe 1−x NiSi (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied using ... more The magnetic properties of Mn x Fe 1−x NiSi (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied using density functional theory and the WIEN2k package. The exchange correlation potential is treated by generalized gradient approximation (GGA). The total energy calculations of these alloys confirm the stability of the ferromagnetic phase as compared to a nonmagnetic phase. The total magnetic moment is not a linear function of x. By increasing x, it increases and then decreases. The peak position of the magnetic moment is near x = 0.75.

Thin Solid Films, Apr 1, 2014

ABSTRACT

Computational Condensed Matter, Dec 1, 2019

Abstract The AlNi intermetallic compound is one of the most promising engineering materials for h... more Abstract The AlNi intermetallic compound is one of the most promising engineering materials for high temperature applications. Unfortunately, this compound has low tensile ductility at high temperature which limit its functional applications. We show that alloying the AlNi compound with the Cr or V will improve its tensile ductility and therefore its industrial applications. In this paper, the structural, electronic, elastic and thermodynamic properties of Al1-xZxNi (Z = Cr, V and x = 0, 0.125, 0.25) alloys have been studied by the first principles calculations in the framework of density functional theory. The calculated formation energy and cohesive energy of the alloys show that, all alloys have stable structures. The valence charge density distribution study reveals that, chemical bonds between the Z and Ni atoms in the alloys have the nature of covalent, which improve the brittleness of the AlNi alloys. The calculated Pugh’s ratio (or the Poisson’s ratio), shear and bulk modules show that, the increasing of hardness by increasing the x. Moreover, the ductility of the alloys decreased when the value of x is nonzero. The calculation results show that the Pugh’s (Poisson’s) ratio is higher than 1.75 (0.26), indicating a ductile nature of these alloys. Furthermore, thermodynamic properties of the alloys including Gruneisen parameter, thermal expansion coefficient, bulk modulus, Debye temperature and constant volume heat capacity have been investigated and discussed under different pressures and temperatures.

Journal of Computational and Theoretical Nanoscience, Aug 1, 2012

ABSTRACT In this letter we performed ab initio calculations on the perfect and defected (5, 5) si... more ABSTRACT In this letter we performed ab initio calculations on the perfect and defected (5, 5) single walled carbon nanotube (SWNT) with Stone Wales (SW) defects. The band structure, density of state (DOS) and wave functions of a long (5, 5) carbon nanotube are calculated. Our results show that, due to the SW defect, the Band structure and DOS of SWNT changed significantly and the metallic behavior of (5, 5) o-SWNT changed to a semiconductor behavior. This confirms that SW defects can drastically change the electronic structures and transport properties of SWNTs.

Journal of Superconductivity and Novel Magnetism, Aug 21, 2014

The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spi... more The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spin orbit coupling using density functional theory using the WIEN2k package are investigated. The stable phase of TbN and ErN bulk using generalized gradient approximation (GGA) approach is studied. The total and partial electron density of states of ErN and TbN nanolayers with two different thicknesses in ferromagnetic phase within GGA and Engel–Vosko GGA (GGA_EV) approaches is calculated. The total and local magnetic moments of these nanolayers are studied. The calculated magnetic moment at Er atomic position of ErN nanolayer is larger than the corresponding value at Tb atomic position of TbN nanolayer. Furthermore, the real and imaginary parts of the dielectric function and the reflectivity and absorption spectra of these nanolayers within GGA_EV approach are studied.

Molecular Physics, Dec 1, 2013

Gas sensing is one of the most promising applications for graphene. Using molecular dynamics simu... more Gas sensing is one of the most promising applications for graphene. Using molecular dynamics simulation method, adsorption isotherm of xenon (Xe) gas on defected and perfect graphene is studied in order to investigate sensing properties of graphene for Xe gas. In this method, first generation of Brenner many-body potential is used to simulate the interaction of carbon–carbon (C) atoms in graphene, and Lennard–Jones two-body potential is used to simulate interaction of Xe–Xe and Xe–C atoms. In the simulated systems, adsorption coverage, radial distribution function, heat of adsorption, binding energy and specific heat capacity at constant volume are calculated for several temperatures between 90 K and 130 K, and various pressures. It was found that both of the defected and perfect graphene could be introduced as very good candidates for adsorption of Xe gas.

Journal of Superconductivity and Novel Magnetism, Sep 3, 2014

In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investiga... more In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investigated in the presence of spin-orbit coupling using density functional theory by Wien2k package. The total energy of ErP and ErSb nanolayers as a function of unit cell volume is calculated in ferromagnetic and nonmagnetic phases using generalized gradient approximation (GGA) approach. It is seen that at zero pressure, the ferromagnetic phase is more stable than nonmagnetic phase. The density of states (DOS) calculation shows that the major contribution to the occupied part of DOS around the Fermi energy comes from 4f orbital of Er and p orbital of P and Sb atoms. The dielectric functions and other optical properties of these compounds have anisotropic behavior. The maximum reflectivity of these nanolayers occurs in the ultraviolet range; then, these nanolayers could be good candidates for shielding ultraviolet radiations.

Advanced Quantum Technologies

Journal of Alloys and Compounds, 2021

Abstract The partial atomic volume of hydrogen, vH, is a fundamentally important thermodynamic pa... more Abstract The partial atomic volume of hydrogen, vH, is a fundamentally important thermodynamic parameter of interstitial metal hydrides in which dissociated H occupies interstices in the metal lattice. Such an important property should be able to be reliably calculated by a suitable theory or model in order to explain and understand its origin. In practice, vH is typically obtained by means of ab initio calculations founded on density functional theory (DFT), where the equilibrium lattice constant at zero temperature is found by minimising the Born-Oppenheimer energy. While the absolute lattice constants calculated in this way depend quite strongly on the DFT scheme employed, the present work showed that vH is rather robust against differing calculational approaches, thus making a meaningful comparison of theory and experiment possible. Comparing vH for PdnH (0

International Journal of Hydrogen Energy, 2021

Systematic test of pseudopotential choice for DFT calculations of MH systems. Four PdH x structur... more Systematic test of pseudopotential choice for DFT calculations of MH systems. Four PdH x structures considered: PdH(oct); PdH(tet); Pd 3 VacH 4 (oct); Pd 3 VacH 4 (tet). Six DFT schemes employed: LDA, PBE and PBESol, with USPP and PAW pseudopotentials. Lattice constants calculated for tet polymporphs have not been found experimentally. Pd 3 VacH 4 (oct) is dynamically unstable in the harmonic approximation.

Journal of Applied Physics, 2020

Topological materials are considered as a novel quantum state of matter, which can be characteriz... more Topological materials are considered as a novel quantum state of matter, which can be characterized by symmetry-protected Dirac interfacial states, and exhibit an exotic phenomenon when combined with the other phases. The topological phase in the perovskite structures is important since it can provide various heterostructure interfaces with multifunctional properties. Alpha-(α-) phase cesium-based halide perovskites CsSnX3 (X = I, Br, Cl) can be considered as a promising candidate for topological semiconductors under hydrostatic pressures. The narrow bandgap of these compounds (≤1.83 eV) has made them interesting materials for the electronic, optoelectronic, and photovoltaic applications. In the current research, we systematically carry out first-principles density functional theory (DFT) to study the effects of hydrostatic pressure on the electronic structure of CsSnX3 (X = I, Br, Cl) compounds. The topological phase of these compositions is investigated using the Fu–Kane and Wilso...

Physica E: Low-dimensional Systems and Nanostructures, 2018

In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNi... more In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNiX (X= Ga and In) half-Heusler compounds have been studied. The calculations have been done based on the density functional theory in the framework of the Wien2k package. The generalized gradient approximation was used for the exchange-correlation functional. Electronic structures and density of states of the bulks and NLs of the compounds show that, they are nonmagnetic and metal. It is found that, the bulks of compounds don't have topological phase, but the NLs of compounds have topological phase. Thus, the NLs of both compounds are topological metals. Important optical properties of these compounds were acquired. The results show that, there is optical anisotropy in the NLs, between the in-plane (x) and out-of-plane (z) directions. The absorptions of the bulks and NLs of the compounds are high in the UV range.

Journal of Magnetism and Magnetic Materials, 2018

Topological insulators are novel state of quantum matter that have a bulk band gap like an ordina... more Topological insulators are novel state of quantum matter that have a bulk band gap like an ordinary insulator, but have protected conducting states by time reversal symmetry on their edge or surface. The spin-orbit coupling can play an important role in these materials, resulting in a band inversion at time reversal invariant momenta (TRIM) points. The topological phase and the effect of the hydrostatic pressure on the electronic structure and topological phase of the KNa 2 Sb compound are investigated by using both first-principles calculations and abinitio based tight-binding computations. Under hydrostatic lattice strain until 5.6%, the KNa 2 Sb compound is semimetal with zero energy band gap and has an inverted band order. In this pressure, the Z 2 invariants of this compound are calculated using the parity analysis at TRIM points and evolution of wannier charge centers at the six TRIM plane. The calculated surface states at (0 0 1) surface show a single Dirac cone exists on the X W Γ¯line at the surface Brillouin zone. To investigate the stability of KNa 2 Sb compound the phonon dispersions and elastic tensors of this compound in the cubic structure are calculated.

Indian Journal of Physics, 2018

Functionalized graphene sheets have attracted increasing attention due to their novel micro-/nano... more Functionalized graphene sheets have attracted increasing attention due to their novel micro-/nano-electromechanical applications. In this paper, the aggregation of the gold nano-clusters on the defected graphene sheet is studied by using the molecular dynamics simulation method. It is shown that a model defected graphene with randomly distributed vacancies can affect the formation and aggregation of the Au nano-clusters on the graphene sheet. It is found that the Au nano-clusters agglomerate on the pristine parts of the surface rather than on the defected parts. In addition, the results show that increasing the temperature amplifies the above result and varies the Au nano-cluster sizes. Moreover, it is observed that the aggregation of Au clusters changes the surface roughness. The results presented here would help to design more efficient functionalized graphene-based electronic devices.

Chinese Physics B, 2016

In this work we propose a two-dimensional carbon-nitrogen allotrope composed of pentagons and oct... more In this work we propose a two-dimensional carbon-nitrogen allotrope composed of pentagons and octagons in a structure of carbon chains bound by nitrogen dimers. Our first-principles calculations show the system behaves as a small-gap semiconductor which is thermodynamically stable at room temperature confirmed by molecular dynamic simulations. By cutting the sheet along different crystallographic directions, a variety of metallic or semiconductor one-dimensional ribbons can be obtained. We explore the topological properties of these nanoribbons finding that for a particular boundary geometry nontrivial topological phases can be obtained, depending on the ribbon termination. We investigate the emergence of symmetry protected interface topological states in heterojunctions and topological-induced edge states in finite ribbons.

Journal of Superconductivity and Novel Magnetism, 2014

In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investiga... more In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investigated in the presence of spin-orbit coupling using density functional theory by Wien2k package. The total energy of ErP and ErSb nanolayers as a function of unit cell volume is calculated in ferromagnetic and nonmagnetic phases using generalized gradient approximation (GGA) approach. It is seen that at zero pressure, the ferromagnetic phase is more stable than nonmagnetic phase. The density of states (DOS) calculation shows that the major contribution to the occupied part of DOS around the Fermi energy comes from 4f orbital of Er and p orbital of P and Sb atoms. The dielectric functions and other optical properties of these compounds have anisotropic behavior. The maximum reflectivity of these nanolayers occurs in the ultraviolet range; then, these nanolayers could be good candidates for shielding ultraviolet radiations.

Journal of Superconductivity and Novel Magnetism, 2014

The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spi... more The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spin orbit coupling using density functional theory using the WIEN2k package are investigated. The stable phase of TbN and ErN bulk using generalized gradient approximation (GGA) approach is studied. The total and partial electron density of states of ErN and TbN nanolayers with two different thicknesses in ferromagnetic phase within GGA and Engel–Vosko GGA (GGA_EV) approaches is calculated. The total and local magnetic moments of these nanolayers are studied. The calculated magnetic moment at Er atomic position of ErN nanolayer is larger than the corresponding value at Tb atomic position of TbN nanolayer. Furthermore, the real and imaginary parts of the dielectric function and the reflectivity and absorption spectra of these nanolayers within GGA_EV approach are studied.

Physica E-low-dimensional Systems & Nanostructures, Sep 1, 2018

In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNi... more In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNiX (X= Ga and In) half-Heusler compounds have been studied. The calculations have been done based on the density functional theory in the framework of the Wien2k package. The generalized gradient approximation was used for the exchange-correlation functional. Electronic structures and density of states of the bulks and NLs of the compounds show that, they are nonmagnetic and metal. It is found that, the bulks of compounds don't have topological phase, but the NLs of compounds have topological phase. Thus, the NLs of both compounds are topological metals. Important optical properties of these compounds were acquired. The results show that, there is optical anisotropy in the NLs, between the in-plane (x) and out-of-plane (z) directions. The absorptions of the bulks and NLs of the compounds are high in the UV range.

Chinese Physics B, Dec 1, 2013

ABSTRACT

Chemical Physics Letters, Apr 1, 2007

Molecular dynamics (MD) simulation is used to compute the adsorption isotherms of xenon (Xe) gas ... more Molecular dynamics (MD) simulation is used to compute the adsorption isotherms of xenon (Xe) gas on defected open ended singlewalled nanotubes (o-SWNT). We perform a simulation based on a many-body interatomic Brenner potential with a two-body interatomic Lennard-Jones (LJ) potential. Adsorption isotherms of Xe on (10, 10) o-SWNT for several temperatures, between 95 and 130 K, are measured. Adsorption coverage, isosteric heat, and binding energy were calculated at various temperatures and pressures and compared with the same properties for the perfect (10, 10) o-SWNT. It is shown that adsorption occurs both inside and outside of an o-SWNTs.

Journal of Superconductivity and Novel Magnetism, Dec 20, 2012

The magnetic properties of Mn x Fe 1−x NiSi (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied using ... more The magnetic properties of Mn x Fe 1−x NiSi (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied using density functional theory and the WIEN2k package. The exchange correlation potential is treated by generalized gradient approximation (GGA). The total energy calculations of these alloys confirm the stability of the ferromagnetic phase as compared to a nonmagnetic phase. The total magnetic moment is not a linear function of x. By increasing x, it increases and then decreases. The peak position of the magnetic moment is near x = 0.75.

Thin Solid Films, Apr 1, 2014

ABSTRACT

Computational Condensed Matter, Dec 1, 2019

Abstract The AlNi intermetallic compound is one of the most promising engineering materials for h... more Abstract The AlNi intermetallic compound is one of the most promising engineering materials for high temperature applications. Unfortunately, this compound has low tensile ductility at high temperature which limit its functional applications. We show that alloying the AlNi compound with the Cr or V will improve its tensile ductility and therefore its industrial applications. In this paper, the structural, electronic, elastic and thermodynamic properties of Al1-xZxNi (Z = Cr, V and x = 0, 0.125, 0.25) alloys have been studied by the first principles calculations in the framework of density functional theory. The calculated formation energy and cohesive energy of the alloys show that, all alloys have stable structures. The valence charge density distribution study reveals that, chemical bonds between the Z and Ni atoms in the alloys have the nature of covalent, which improve the brittleness of the AlNi alloys. The calculated Pugh’s ratio (or the Poisson’s ratio), shear and bulk modules show that, the increasing of hardness by increasing the x. Moreover, the ductility of the alloys decreased when the value of x is nonzero. The calculation results show that the Pugh’s (Poisson’s) ratio is higher than 1.75 (0.26), indicating a ductile nature of these alloys. Furthermore, thermodynamic properties of the alloys including Gruneisen parameter, thermal expansion coefficient, bulk modulus, Debye temperature and constant volume heat capacity have been investigated and discussed under different pressures and temperatures.

Journal of Computational and Theoretical Nanoscience, Aug 1, 2012

ABSTRACT In this letter we performed ab initio calculations on the perfect and defected (5, 5) si... more ABSTRACT In this letter we performed ab initio calculations on the perfect and defected (5, 5) single walled carbon nanotube (SWNT) with Stone Wales (SW) defects. The band structure, density of state (DOS) and wave functions of a long (5, 5) carbon nanotube are calculated. Our results show that, due to the SW defect, the Band structure and DOS of SWNT changed significantly and the metallic behavior of (5, 5) o-SWNT changed to a semiconductor behavior. This confirms that SW defects can drastically change the electronic structures and transport properties of SWNTs.

Journal of Superconductivity and Novel Magnetism, Aug 21, 2014

The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spi... more The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spin orbit coupling using density functional theory using the WIEN2k package are investigated. The stable phase of TbN and ErN bulk using generalized gradient approximation (GGA) approach is studied. The total and partial electron density of states of ErN and TbN nanolayers with two different thicknesses in ferromagnetic phase within GGA and Engel–Vosko GGA (GGA_EV) approaches is calculated. The total and local magnetic moments of these nanolayers are studied. The calculated magnetic moment at Er atomic position of ErN nanolayer is larger than the corresponding value at Tb atomic position of TbN nanolayer. Furthermore, the real and imaginary parts of the dielectric function and the reflectivity and absorption spectra of these nanolayers within GGA_EV approach are studied.

Molecular Physics, Dec 1, 2013

Gas sensing is one of the most promising applications for graphene. Using molecular dynamics simu... more Gas sensing is one of the most promising applications for graphene. Using molecular dynamics simulation method, adsorption isotherm of xenon (Xe) gas on defected and perfect graphene is studied in order to investigate sensing properties of graphene for Xe gas. In this method, first generation of Brenner many-body potential is used to simulate the interaction of carbon–carbon (C) atoms in graphene, and Lennard–Jones two-body potential is used to simulate interaction of Xe–Xe and Xe–C atoms. In the simulated systems, adsorption coverage, radial distribution function, heat of adsorption, binding energy and specific heat capacity at constant volume are calculated for several temperatures between 90 K and 130 K, and various pressures. It was found that both of the defected and perfect graphene could be introduced as very good candidates for adsorption of Xe gas.

Journal of Superconductivity and Novel Magnetism, Sep 3, 2014

In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investiga... more In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investigated in the presence of spin-orbit coupling using density functional theory by Wien2k package. The total energy of ErP and ErSb nanolayers as a function of unit cell volume is calculated in ferromagnetic and nonmagnetic phases using generalized gradient approximation (GGA) approach. It is seen that at zero pressure, the ferromagnetic phase is more stable than nonmagnetic phase. The density of states (DOS) calculation shows that the major contribution to the occupied part of DOS around the Fermi energy comes from 4f orbital of Er and p orbital of P and Sb atoms. The dielectric functions and other optical properties of these compounds have anisotropic behavior. The maximum reflectivity of these nanolayers occurs in the ultraviolet range; then, these nanolayers could be good candidates for shielding ultraviolet radiations.

Advanced Quantum Technologies

Journal of Alloys and Compounds, 2021

Abstract The partial atomic volume of hydrogen, vH, is a fundamentally important thermodynamic pa... more Abstract The partial atomic volume of hydrogen, vH, is a fundamentally important thermodynamic parameter of interstitial metal hydrides in which dissociated H occupies interstices in the metal lattice. Such an important property should be able to be reliably calculated by a suitable theory or model in order to explain and understand its origin. In practice, vH is typically obtained by means of ab initio calculations founded on density functional theory (DFT), where the equilibrium lattice constant at zero temperature is found by minimising the Born-Oppenheimer energy. While the absolute lattice constants calculated in this way depend quite strongly on the DFT scheme employed, the present work showed that vH is rather robust against differing calculational approaches, thus making a meaningful comparison of theory and experiment possible. Comparing vH for PdnH (0

International Journal of Hydrogen Energy, 2021

Systematic test of pseudopotential choice for DFT calculations of MH systems. Four PdH x structur... more Systematic test of pseudopotential choice for DFT calculations of MH systems. Four PdH x structures considered: PdH(oct); PdH(tet); Pd 3 VacH 4 (oct); Pd 3 VacH 4 (tet). Six DFT schemes employed: LDA, PBE and PBESol, with USPP and PAW pseudopotentials. Lattice constants calculated for tet polymporphs have not been found experimentally. Pd 3 VacH 4 (oct) is dynamically unstable in the harmonic approximation.

Journal of Applied Physics, 2020

Topological materials are considered as a novel quantum state of matter, which can be characteriz... more Topological materials are considered as a novel quantum state of matter, which can be characterized by symmetry-protected Dirac interfacial states, and exhibit an exotic phenomenon when combined with the other phases. The topological phase in the perovskite structures is important since it can provide various heterostructure interfaces with multifunctional properties. Alpha-(α-) phase cesium-based halide perovskites CsSnX3 (X = I, Br, Cl) can be considered as a promising candidate for topological semiconductors under hydrostatic pressures. The narrow bandgap of these compounds (≤1.83 eV) has made them interesting materials for the electronic, optoelectronic, and photovoltaic applications. In the current research, we systematically carry out first-principles density functional theory (DFT) to study the effects of hydrostatic pressure on the electronic structure of CsSnX3 (X = I, Br, Cl) compounds. The topological phase of these compositions is investigated using the Fu–Kane and Wilso...

Physica E: Low-dimensional Systems and Nanostructures, 2018

In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNi... more In this paper, topological phase and optical properties of bulks and nanolayers (NLs) of the ScNiX (X= Ga and In) half-Heusler compounds have been studied. The calculations have been done based on the density functional theory in the framework of the Wien2k package. The generalized gradient approximation was used for the exchange-correlation functional. Electronic structures and density of states of the bulks and NLs of the compounds show that, they are nonmagnetic and metal. It is found that, the bulks of compounds don't have topological phase, but the NLs of compounds have topological phase. Thus, the NLs of both compounds are topological metals. Important optical properties of these compounds were acquired. The results show that, there is optical anisotropy in the NLs, between the in-plane (x) and out-of-plane (z) directions. The absorptions of the bulks and NLs of the compounds are high in the UV range.

Journal of Magnetism and Magnetic Materials, 2018

Topological insulators are novel state of quantum matter that have a bulk band gap like an ordina... more Topological insulators are novel state of quantum matter that have a bulk band gap like an ordinary insulator, but have protected conducting states by time reversal symmetry on their edge or surface. The spin-orbit coupling can play an important role in these materials, resulting in a band inversion at time reversal invariant momenta (TRIM) points. The topological phase and the effect of the hydrostatic pressure on the electronic structure and topological phase of the KNa 2 Sb compound are investigated by using both first-principles calculations and abinitio based tight-binding computations. Under hydrostatic lattice strain until 5.6%, the KNa 2 Sb compound is semimetal with zero energy band gap and has an inverted band order. In this pressure, the Z 2 invariants of this compound are calculated using the parity analysis at TRIM points and evolution of wannier charge centers at the six TRIM plane. The calculated surface states at (0 0 1) surface show a single Dirac cone exists on the X W Γ¯line at the surface Brillouin zone. To investigate the stability of KNa 2 Sb compound the phonon dispersions and elastic tensors of this compound in the cubic structure are calculated.

Indian Journal of Physics, 2018

Functionalized graphene sheets have attracted increasing attention due to their novel micro-/nano... more Functionalized graphene sheets have attracted increasing attention due to their novel micro-/nano-electromechanical applications. In this paper, the aggregation of the gold nano-clusters on the defected graphene sheet is studied by using the molecular dynamics simulation method. It is shown that a model defected graphene with randomly distributed vacancies can affect the formation and aggregation of the Au nano-clusters on the graphene sheet. It is found that the Au nano-clusters agglomerate on the pristine parts of the surface rather than on the defected parts. In addition, the results show that increasing the temperature amplifies the above result and varies the Au nano-cluster sizes. Moreover, it is observed that the aggregation of Au clusters changes the surface roughness. The results presented here would help to design more efficient functionalized graphene-based electronic devices.

Chinese Physics B, 2016

In this work we propose a two-dimensional carbon-nitrogen allotrope composed of pentagons and oct... more In this work we propose a two-dimensional carbon-nitrogen allotrope composed of pentagons and octagons in a structure of carbon chains bound by nitrogen dimers. Our first-principles calculations show the system behaves as a small-gap semiconductor which is thermodynamically stable at room temperature confirmed by molecular dynamic simulations. By cutting the sheet along different crystallographic directions, a variety of metallic or semiconductor one-dimensional ribbons can be obtained. We explore the topological properties of these nanoribbons finding that for a particular boundary geometry nontrivial topological phases can be obtained, depending on the ribbon termination. We investigate the emergence of symmetry protected interface topological states in heterojunctions and topological-induced edge states in finite ribbons.

Journal of Superconductivity and Novel Magnetism, 2014

In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investiga... more In this paper, the magnetic and optical properties of ErP and ErSb nanolayers have been investigated in the presence of spin-orbit coupling using density functional theory by Wien2k package. The total energy of ErP and ErSb nanolayers as a function of unit cell volume is calculated in ferromagnetic and nonmagnetic phases using generalized gradient approximation (GGA) approach. It is seen that at zero pressure, the ferromagnetic phase is more stable than nonmagnetic phase. The density of states (DOS) calculation shows that the major contribution to the occupied part of DOS around the Fermi energy comes from 4f orbital of Er and p orbital of P and Sb atoms. The dielectric functions and other optical properties of these compounds have anisotropic behavior. The maximum reflectivity of these nanolayers occurs in the ultraviolet range; then, these nanolayers could be good candidates for shielding ultraviolet radiations.

Journal of Superconductivity and Novel Magnetism, 2014

The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spi... more The electronic, magnetic, and optical properties of TbN and ErN nanolayers in the presence of spin orbit coupling using density functional theory using the WIEN2k package are investigated. The stable phase of TbN and ErN bulk using generalized gradient approximation (GGA) approach is studied. The total and partial electron density of states of ErN and TbN nanolayers with two different thicknesses in ferromagnetic phase within GGA and Engel–Vosko GGA (GGA_EV) approaches is calculated. The total and local magnetic moments of these nanolayers are studied. The calculated magnetic moment at Er atomic position of ErN nanolayer is larger than the corresponding value at Tb atomic position of TbN nanolayer. Furthermore, the real and imaginary parts of the dielectric function and the reflectivity and absorption spectra of these nanolayers within GGA_EV approach are studied.