共查询到20条相似文献,搜索用时 500 毫秒
1.
Gökhan Göko?lu 《Journal of Physics and Chemistry of Solids》2010,71(9):1388-1392
The lattice dynamics of large-gap semiconductor MgTe compound at various crystallographic phases; rocksalt (B1), zincblende (B3), NiAs (B81) and wurtzite (B4), has been investigated from first principles calculations based on density functional theory (DFT) within plane-wave pseudopotential method and generalized gradient approximation (GGA) of the exchange-correlation functional. The static equation of states of the compound has been studied with Vinet equation of states. The ground state of the compound is a fourfold coordinated wurtzite structure, which is consistent with experiments and recent theoretical calculations. Full phonon dispersion spectra of all related phases of the MgTe have been calculated using density functional perturbation theory within the linear-response approach. In view of the total energy calculations and the obtained vibrational spectra, it can be emphasized that the MgTe polymorphs with tetrahedral coordination (zincblende and wurtzite structures) are of covalent character rather than ionic. The large TO-LO splitting of phonon branches of rocksalt and NiAs phases reflect the high ionicity of these phases. 相似文献
2.
A. H. Reshak Z. Charifi H. Baaziz 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):463-468
We present the results of the ab initio theoretical study of the optical properties for PbFX (X = Cl, Br, I) compounds in its matlockite-type structure using the
full potential linearized augmented plane wave (FP-LAPW) method as
implemented in the WIEN2K code. We employed generalized gradient
approximation (GGA), which is based on exchange-correlation energy
optimization to calculate the total energy. Also we have used the
Engel-Vosko GGA formalism, which optimizes the corresponding potential for
band structure calculations. Our calculations show that the valence band
maximum (VBM) and conduction band minimum (CBM) are located at Z resulting
in a direct energy gap. We present calculations of the frequency-dependent
complex dielectric function ε( ω) and its
zero-frequency limit ε1 ( 0 ). We find that the
values of ε1 ( 0 ) increases with decreasing the
energy gap. The reflectivity spectra and absorption coefficient has been
calculated and compared with the available experimental data. The optical
properties are analyzed and the origin of some of the peaks in the spectra
is discussed in terms of the calculated electronic structure. 相似文献
3.
Structural, elastic and electronic properties of strontium chalcogenides SrX (X = O, S and Se) in the B1 (NaCl) and B2 (CsCl) phases were investigated in the present work. The calculations were performed using density functional theory (DFT) within generalized gradient approximation (GGA) using scalar relativistic Vanderbilt-type ultrasoft pseudopotentials. Results for structural properties of both phases, the pressure at which transition from B1 to B2 phase occurs and the volume compression ratio for each compound were reported. Elastic properties of the B1 phase of these compounds, such as elastic constants C11, C12, and C44, shear modulus (G), Young's modulus (E), Poisson's ratio (σ), Kleinman parameter (ξ), and anisotropy factor (A) were also calculated at ambient conditions. The band gaps and density of states were studied too for the B1 structure of these compounds. The present results were compared with the available experimental and other theoretical results, and found to be in satisfactory agreement with them. 相似文献
4.
M. Lemmer B. Hilling M. Wöhlecke M. Imlau A. A. Lebedev V. V. Bryksin M. P. Petrov 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(1):9-14
The structural parameters and hydrostatic pressure coefficients of
CdSxTe1-x in the two phases, namely zinc-blende and NaCl as well
as the transition pressures from zinc-blende to NaCl structures at various S
concentrations are presented. The calculations are performed using the full
potential linearized augmented plane wave (FP-LAPW) method within the
density functional theory (DFT) in the local density approximation (LDA),
and two developed refinements, namely the generalized gradient approximation
(GGA) of Perdew et al. for the structural properties and
Engel-Vosko for the band structure calculations. Detailed
comparisons are made with published experimental and theoretical data and
show generally good agreement. The present results regarding the studied
quantities for compositions x in the 0–1 range (0 < x < 1) and for the NaCl
phase are predictions and may serve as a reference for experimental work. 相似文献
5.
H. Salehi N. Shahtahmasebi S.M. Hosseini 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):177-180
The electronic structure, total density of states DOS and electronic density in ferroelectric tetragonal crystal BaTiO3 are studied using WIEN2k package. This employs the full potential-linearized augmented plan wave FP-LAPW method in the framework
of the density functional theory DFT with the generalized gradient approximation (GGA). The results show an indirect band
gap of 2.30 eV at the Γ point in the Brillouin zone. The calculated band structure and density of states of BaTiO3 agree with the previous experimental and theoretical results, as do the charge distribution and the prediction of the nature
of the chemical bonding.
Received 11 December 2002 / Received in final form 3 February 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: salehihamid@yahoo.com 相似文献
6.
M. Moakafi R. Khenata A. Bouhemadou H. Khachai B. Amrani D. Rached M. Rérat 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):35-42
We report results of first-principles calculations for the electronic and optical properties under pressure effect of Li2O, Na2O, Ki2O and Rb2O compounds in the cubic antifluorite structure, using a full relativistic version of the full-potential augmented plane-wave
plus local orbitals (FP-APW+lo) method based on density functional theory, within the local density approximation (LDA) and
the generalized gradient approximation (GGA). Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is
also used for band structure calculations. The calculated equilibrium lattices and bulk moduli are in good agreement with
the available data. Band structure, density of states, and pressure coefficients of the fundamental energy gap are given.
The critical point structure of the frequency dependent complex dielectric function is also calculated and analyzed to identify
the optical transitions. The pressure dependence of the static optical dielectric constant is also investigated. 相似文献
7.
We have presented results on the electronic structure and the electric field gradient (EFG) of NpRh3 within a framework of density functional theory within the local density approximation (LDA) and generalized gradient approximation (GGA) with and without spin-orbit coupling (SOC). The electronic density of states (DOS) shows that Np-f to Rh-d hybridization leads to a narrow band 5f-electron. Using the GGA and spinpolarized calculations, the calculated EFG shows that the dominant contribution to EFG comes from electrons with strong p-character. 相似文献
8.
Mohammed El Amine Monir 《哲学杂志》2020,100(19):2524-2539
ABSTRACT Based on the full-potential linearised augmented plane wave plus local orbitals (FP-L/APW?+?lo) method within the density functional theory (DFT), the structural, electronic, and magnetic calculations of the cubic oxide perovskite NdInO3 compound have been done under the generalised gradient approximation (GGA). The exchange and correlation (XC) potential is defined as GGA framework in the analyses of structural properties, while both GGA and GGA?+?U (U is the Hubbard correlation term) approximations are taken to treat the electronic and magnetic properties. It is found that ferromagnetic (FM) configuration is reported as the most stable ground state of the cubic NdInO3 material; however, the equilibrium lattice parameters such as lattice constant (a0 ), bulk modulus (B0 ), its first-pressure derivative (B’), and the minimum of total energy (E0 ) are given in paramagnetic (PM), ferromagnetic (FM), and anti-ferromagnetic (AFM) states. The spin-polarized electronic structure calculations (band structure and density of states) of the cubic oxide perovskite NdInO3 compound verify the half-metallic feature due to the spin-up case which has the metallic nature, whereas the spin-down case presents the semiconducting character. Moreover, the magnetic properties show the integer value of the total magnetic moment for the studied compound (3μB ), where it is manly contributed by Nd atoms with apparition of weak local magnetic moments in non magnetic In and O sites. 相似文献
9.
Y. Benmimoun A. Bouhemadou R. Khenata A. H. Reshak B. Amrani M. Ameri H. Baltache 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):165-171
The results of first-principles theoretical study of the structural,
electronic and optical properties of SrCl2 in its cubic structure, have
been performed using the full-potential linear augmented plane-wave method
plus local orbitals (FP-APW+lo) as implemented in the WIEN2k code. In this
approach both the local density approximation (LDA) and the generalized
gradient approximation (GGA) are used for the exchange-correlation (XC)
potential. Also we have used the Engel-Vosko GGA formalism, which optimizes
the corresponding potential for band structure calculations. We performed
these calculations with and without spin-orbit interactions. Including
spin-orbit coupling cause to lifts the triple degeneracy at Γ point
and a double degeneracy at X point. Results are given for structural
properties. The pressure dependence of elastic constants and band gaps are
investigated. The dielectric function, reflectivity spectra and refractive
index are calculated up to 30 eV. Also we calculated the pressure and volume
dependence of the static optical dielectric constant. 相似文献
10.
We have studied the structural, electronic and phonon properties of the YP and YAs compounds in NaCl(B1) and CsCl(B2) structures using the density functional theory within the generalized gradient approximation (GGA). The calculated lattice constants, static bulk modulus, first-order pressure derivative of the bulk modulus and transition pressure are reported and compared with previous calculations. We have carried out the calculations of band structure and density of states (DOS) for YP and YAs. Then, a linear-response approach to the density-functional theory is used to derive the phonon frequencies and DOS in both B1 and B2 structures. 相似文献
11.
Suleyman Cabuk 《Central European Journal of Physics》2012,10(1):239-252
The nonlinear optical properties of some ABO3 materials (BaTiO3, KNbO3, LiTaO3 and LiNbO3) are studied by density functional theory (DFT) in the local density approximation (LDA) expressions based on first-principle
calculations. Our goals are to give the details of the calculations for linear and nonlinear optical properties, including
the linear electro-optic (EO) tensor for some ABO3 structures with oxygen octahedral structures using first-principles methods. These results can then be used in the study
of the physics of ferroelectrics, specifically, we present calculations of the second harmonic generation response coefficient
X
ijk
(2) (−2ω, ω, ω) over a large frequency range for ABO3 crystals. The electronic linear EO susceptibility X
ijk
(2) (−ω, ω,0) is also evaluated below the band gap. These results are based on a series of the LDA calculations using DFT. Results for
X
ijk
(2) (−ω, ω,0) are in agreement with experiments below the band gap. The results are compared with the theoretical calculations and the
available experimental data. 相似文献
12.
M. Guemou B. BouhafsA. Abdiche R. KhenataY. Al Douri S. Bin Omran 《Physica B: Condensed Matter》2012,407(8):1292-1300
Density functional calculations are performed to study the structural, electronic and optical properties of technologically important BxGa1−xAs ternary alloys. The calculations are based on the total-energy calculations within the full-potential augmented plane-wave (FP-LAPW) method. For exchange-correlation potential, local density approximation (LDA) and the generalized gradient approximation (GGA) have been used. The structural properties, including lattice constants, bulk modulus and their pressure derivatives, are in very good agreement with the available experimental and theoretical data. The electronic band structure, density of states for the binary compounds and their ternary alloys are given. The dielectric function and the refractive index are also calculated using different models. The obtained results compare very well with previous calculations and experimental measurements. 相似文献
13.
The density functional theory (DFT) calculations of structural, elastic, electronic and optical properties of the cubic antiperovskite AsNMg3 has been reported using the pseudo-potential plane wave method (PP-PW) within the generalized gradient approximation (GGA). The equilibrium lattice, bulk modulus and its pressure derivative have been determined. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline AsNMg3 aggregate. We estimated the Debye temperature of AsNMg3 from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNMg3 compound, and it still awaits experimental confirmation. Band structure, density of states and pressure coefficients of energy gaps are also given. The fundamental band gap (Γ-Γ) initially increases up to 4 GPa and then decreases as a function of pressure. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. The all results are compared with the available theoretical and experimental data. 相似文献
14.
M. Ilkhani M. R. Abolhassani M. Aslaninejad 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(1):21-28
The impacts of pressure on the structural and electronic properties of CeIn3 have been calculated. The calculations are performed in the presence and the absence of spin-orbit interaction as well as
GGA+U using density functional theory within the PBE-GGA approximation. It is shown that energy and density of states analyses
are considerably influenced by the spin-orbit interaction. The spin and orbital magnetic moments of Ce are calculated under
pressure up to 22 GPa. An almost linear relation is observed between the magnetic moment and the density of states of Ce-4f at Fermi level. At ambient pressure, a good agreement between the values of the electric field gradients, EFG, and bulk modulus
with experimental results is observed. The strongest anisotropy in charge distribution originates from In-5p orbital, which has the main contribution to EFG. 相似文献
15.
A. H. Moudden 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):173-183
Several structures for off-stoichiometric beryllium diboride dicarbide Be1−xB2C2 have been designed, and their properties studied from first-principles density functional methods. Among the most stable
phases examined, the layered hexagonal structures are shown to exhibit various features in the electronic properties and in
the lattice dynamics reminiscent of the superconducting magnesium diboride and alkaline earth-intercalated graphites. For
substoichiometric composition x ∼ 1/3, the system is found metallic with a moderately strong electron-phonon coupling through a predominant contribution
arising from high frequency streching modes modulating the σ-bonding of the B-C network, and a weaker contribution at medium frequency range of the phonon spectra, arising from the intercalent
motion coupled to the π-bonding states. Further, anharmonicities emerging from the proximity of the Fermi level to the σ-band edge, contributes to reduce the phonon softening hence stabilizing the structure. All these effects appear to combine
favourably to produce a high temperature phonon-superconductivity. 相似文献
16.
H. Khosroabadi A. Tavana M. Akhavan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):161-165
Ab initio total energy calculations have been performed for superconducting
GdBa2Cu3O7 and insulating PrBa2Cu3O7 using the
full-potential linear augmented plane-wave method in the local density
approximation (LDA) and generalized gradient approximation (GGA). The
comparison of the calculated unit cell volume and lattice parameters with
the experimental data indicates the improvement of these parameters in the
GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about
6% smaller and 1.25% larger than the experimental data, respectively
for both systems. Thus frozen phonon calculations have been performed to
determine the eigenvalues and eigenvectors of the k=0 Ag modes of the
two systems in equilibrium structure have been obtained in GGA. The
calculated frequencies in the GGA are in good agreement with the other LDA
calculations for similar systems. Comparison of computational data with
experimental data indicates that calculations determine the frequencies
about ten percent below the experimental data. Even by improving LDA to GGA
in these calculations, the calculated phonon frequencies have remained
almost ten percent below the experimental data, even though the calculated
unit cell volumes are nearly equal to the experimental data. So, applying
GGA has not considerably decreased the difference between the computational
and experimental data. The effect of Pr doping on the eigenvalues and
eigenvectors have also been investigated. 相似文献
17.
Based on the spin generalized gradient approximation (σGGA) of the density functional theory (DFT), the structural, magnetic, and electronic properties of Mn-doped ZnO structure have thoroughly been investigated. It is found that the Mn atom prefers to substitute one of the Zn atoms, producing the energetically most stable configuration for the Mn-doped ZnO structure. Employing the Hubbard potential within the calculations suggests various changes and modifications to the structural, magnetic and electronic properties of the Mn-doped ZnO. Our calculations reveal that the local magnetic moment at the Mn site using the ordinary σGGA functional is 4.84 μB/Mn, which is smaller than that evaluated by including the Hubbard potential of 5.04 μB/Mn. Overall, the electronic band structure of the system, within the σGGA+U, is half-metallic, with metallic nature for the majority state and semiconducting nature for the minority state. Simulated scanning tunneling microscopy (STM) images for both unoccupied and occupied states indicate siginficant brightness on both Zn and Mn atoms and much brighter protrusions around the O atoms, respectively. 相似文献
18.
Electronic structure calculations based on density functional (DFT) theory within the generalized gradient approximation (GGA) for the Ti2CoGa Heusler compound have been performed using the self-consistent full-potential linearized augmented plane wave (FPLAPW) method. The electronic band structures and density of states of the Ti2CoGa compound show that the spin-up electrons are metallic, but the spin-down bands have a gap of 0.5 eV, resulting in stable half-metallic ferrimagnetic behavior with a magnetic moment of 2μB. 相似文献
19.
Using first-principles density functional theory calculations within the generalised gradient approximation (GGA) as well as GGA+U method we study Ca-doped α-Cr2O3 crystal. Structural, electronic and magnetic properties due to the singular impurity incorporation have been investigated and discussed in detail. Atomic shifts as well as computed Bader charges on atoms imply the importance of ionic nature in the atomic interactions in chromium oxide. The study improves our knowledge on how the crystalline lattice reacts on the presence of a Ca dopant. According to our research it is found that Ca impurity incorporation produces some local changes upon the electronic band structure of the material without occurrence of local states within the band-gap. It is found that Ca incorporation produces change in magnetic behaviour of the crystal: it becomes ferromagnetic. 相似文献
20.
M. R. Galpin D. E. Logan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(2):129-145
We develop a non-perturbative local moment approach (LMA) for the gapped Anderson impurity model (GAIM), in which a locally
correlated orbital is coupled to a host with a gapped density of states.
Two distinct phases arise, separated by a level-crossing quantum phase transition: a screened singlet phase, adiabatically
connected to the non-interacting limit and as such a generalized Fermi liquid (GFL); and an incompletely screened, doubly
degenerate local moment (LM) phase.
On opening a gap (δ) in the host, the transition occurs at a critical gap δc, the GFL [LM] phase occurring for δ<δc [ δ>δc] . In agreement with numerical renormalization group (NRG) calculations, the critical
δc = 0 at the particle-hole symmetric point of the model, where the LM phase arises immediately on opening the gap. In the generic
case by contrast δc > 0, and the resultant LMA phase boundary is in good quantitative agreement with NRG results. Local single-particle dynamics
are considered in some detail.
The major difference between the two phases resides in bound states within the gap: the GFL phase is found to be characterised
by one bound state only, while the LM phase contains two such states straddling the chemical potential. Particular emphasis
is naturally given to the
strongly correlated, Kondo regime of the model. Here,
single-particle dynamics for both phases are found to exhibit universal scaling as a function of scaled frequency ω/ωm
0 for fixed gaps
δ/ωm
0, where ωm
0 is the characteristic Kondo scale for the gapless (metallic) AIM; at particle-hole symmetry in particular, the
scaling spectra are obtained in closed form. For frequencies
|ω|/ωm
0 ≫δ/ωm
0, the
scaling spectra are found generally to reduce to those of the gapless, metallic Anderson model;
such that for small gaps δ/ωm
0≪ 1 in particular, the Kondo resonance that is the spectral hallmark of the usual metallic Anderson model persists more or
less in its entirety in the GAIM. 相似文献