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1.
The optical properties of the SrFX (X=Cl, Br, I) compound have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the 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 Γ 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 value of ε1(0) increases on decreasing the energy gap. The reflectivity spectra and absorption coefficient have been calculated and compared with the available experimental data. 相似文献
2.
A. Shaukat Y. Saeed N. Ikram H. Akbarzadeh 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):439-446
First principles calculations have been performed within the
framework of density functional theory to investigate the structural,
electronic and optical properties of all four possible B1, B2, B3 and B4
phases of CaS. Apart from the standard local density approximation (LDA) and
GGA (PBE), a more accurate nonempirical density functional generalized
gradient approximation (GGA), as proposed by Wu and Cohen [Phys. Rev. B 73,
235116 (2006)] for the exchange-correlation energy, EXC, has been
attempted in these calculations. Calculated electronic structure and the
density of states are analyzed in terms of the contribution of Ca d states
and S s and p states in determining the nature of the fundamental band gap
in various phases. Reflectivity, R (ω), the real and imaginary part
of the dielectric functions, ε(ω), have been
calculated for all the phases and the results have been discussed and
compared with the existing experimental data. 相似文献
3.
The electronic, structural properties and optical properties of the rutile TiO2 have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the 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 results including lattice parameter, bulk modulus, density of states, the reflectivity spectra, the refractive index and band gap are compared with the experimental data. We present calculations of the frequency-dependent complex dielectric function ε(ω) and its zero-frequency limit ε1(0). 相似文献
4.
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
5.
Youcef Bouhadda Youcef Boudouma Abdelouahab Bentabet 《Journal of Physics and Chemistry of Solids》2010,71(9):1264-2326
The structural stability, electronic structure, optical and thermodynamic properties of NaMgH3 have been investigated using the density functional theory. Good agreement is obtained for the bulk crystal structure using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation energy. It is found from the electronic density of states (DOS) that the valence band is dominated by the hydrogen atoms while the conduction band is dominated by Na and Mg empty states. Also, the DOS reveals that NaMgH3 is a large gap insulator with direct band gap 3.4 eV. We have investigated the optical response of NaMgH3 in partial band to band contributions and the theoretical optical spectrum is presented and discussed in this study. Optical response calculation suggests that the imaginary part of dielectric function spectra is assigned to be the interband transition. The formation energy for NaMgH3 is investigated along different reaction pathways. We compare and discuss our result with the measured and calculated enthalpies of formation found in the literature. 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.
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
8.
The electronic structure and the optical properties of In6S7 crystal are calculated by the first-principles full-potential linearized augmented plane wave method (FP-LAPW) using density functional theory (DFT) in its generalized gradient approximation (GGA). The calculated band structure shows that the In6S7 is a semiconductor with a direct band gap in good agreement with experimental studies. Furthermore, the dielectric tensor and the optical properties, such as absorption coefficient, refractive index, extinction coefficient, energy-loss spectrum and reflectivity, are derived and analyzed in the study. 相似文献
9.
We report results of first-principles total-energy calculations for structural properties of the group I-VII silver iodide (AgI) semiconductor compound under pressure for B1 (rocksalt), B2 (cesium chloride), B3 (zinc-blende) and B4 (wurtzite) structures. Calculations have been performed using all-electron full-potential linearized augmented plane wave plus local orbitals FP-LAPW + lo method based on density-functional theory (DFT) and using generalised gradient approximation (GGA) for the purpose of exchange correlation energy functional. In agreement with experimental and earlier ab initio calculations, we find that the B3 phase is slightly lower in energy than the B4 phase, and it transforms to B1 structure at 4.19 GPa. Moreover, we found AgI has direct gap in B3 structure with a band gap of 1.378 eV and indirect band gap in B1 phase with a bandgap around 0.710 eV. We also present results of the effective masses for the electrons in the conduction band (CB) and the holes in the valence band (VB). To complete the fundamental characteristics of this compound we have analyzed their linear optical properties such as the dynamic dielectric function and energy loss function for a wide range of 0-25 eV. 相似文献
10.
M. Debbichi A. Ben Fredj A. Bhouri N. Bouarissa M. Said 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):17-23
Taking into account the recent advances in the epitaxial growth of
single-crystal InN leading to a drastic re-evaluation of its fundamental
energy band gap, we have studied the electronic properties of
InNxP1-x (x < 0.01) ternary alloy. Using the empirical
pseudopotential method under the virtual crystal approximation, combined
with the Harrison bond orbital model, the band gap at Γ, X and L
points, the effective masses of the Γ valley and the electronic
charge densities are calculated as a function of nitrogen composition. The
fitted expressions of the energy band gaps indicate that the bowing
parameter at Γ reached a broad value for very low nitrogen
incorporation (
).
Furthermore, the band gap at Γ point decreases drastically with
increasing nitrogen composition up to 1%. The elastic constants and the
optical phonon frequencies are also reported. Our theoretical results
provide a good agreement with the available data. 相似文献
11.
B. Amrani F. El Haj Hassan H. Akbarzadeh 《Journal of Physics and Chemistry of Solids》2009,70(7):1055-1061
We have performed first-principles calculations using full potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT) to investigate the fundamental properties of CuxAg1−xI alloys. We used both GGA96 [J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865.] and EVGGA [E. Engel, S.H. Vosko, Phys. Rev. B. 47 (1993) 13164.] generalized gradient approximations of the exchange-correlation energy that are based on the optimization of total energy and corresponding potential. Quantities such as lattice constants, bulk modulus, band gap, density of occupied states and effective mass were calculated as a function of copper molar fraction x. These parameters were found to depend non-linearly on alloy composition x, except the lattice parameter, which follows Vegard's law. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers; we have concluded that the band-gap energy bowing was mainly caused by the chemical charge-transfer effect and the volume deformation , while the structural relaxation contribute to the gap bowing parameter at smaller magnitude. The calculated phase diagram shows a broad miscibility gap for this alloy with a high critical temperature. 相似文献
12.
Hao Wang Ying Chen Yasunori Kaneta Shuichi Iwata 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(2):155-165
The Si3N4 and Ge3N4 are important
structural ceramics with many applications because of their
attractive high temperature and oxidation resistant properties. The
high-pressure and high-temperature spinel phases of these two
materials were noticed to have wide, direct electronic band gaps.
Other single and double spinel nitrides formed from IVA and IVB
group elements have also attracted much attention. Present research
focuses on selecting a special substance with promising optical
properties and stability besides the attractive electronic
properties. The formation energies of spinel nitrides are calculated
and stabilities of a group of spinel nitrides are discussed, the
structural and electronic properties of them are investigated in
detail. By random phase approximation (RPA), the optical properties
of spinel nitrides are researched. We obtain that
γ-SiGe2N4 has some promising properties with
potential technological applications from various aspects. The band
transitions which contribute most to the peak of ε2
have been identified. An assumption is proposed to raise the peak of
ε2. 相似文献
13.
Ali H. Reshak S. Auluck I. V. Kityk Y. Al-Douri R. Khenata A. Bouhemadou 《Applied Physics A: Materials Science & Processing》2009,94(2):315-320
We report theoretical calculations of the band structure and density of states for orthorhombic LiGaS2 (LGS) and LiGaSe2 (LGSe). These calculations are based on the full potential linear augmented plane wave (FP-LAPW) method within a framework
of density functional theory. Our calculations show that these crystals have similar band structures. The valence band maximum
(VBM) and the conduction band minimum (CBM) are located at Γ, resulting in a direct energy band gap. The VBM is dominated by S/Se-p and Li-p states, while the CBM is dominated by Ga-s,
S/Se-p and small contributions of Li-p and Ga-p. From the partial density of states we find that Li-p hybridizes with Li-s
below the Fermi energy (E
F), while Li-s/p hybridizes with Ga-p below and above E
F. Also, we note that S/Se-p hybridizes with Ga-s below and above E
F. 相似文献
14.
A.K. Ray J.C. Boettger 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):429-433
The linear combinations of Gaussian type orbitals fitting function (LCGTO-FF) method is used to study the electronic and geometrical
properties of plutonium monolayers with square and hexagonal symmetry. The effects of several common approximations are examined:
(1) scalar-relativity vs. full-relativity (i.e., with spin-orbit coupling included); (2) paramagnetic vs. spin-polarized; and (3) local-density approximation (LDA) vs. generalized- gradient approximation (GGA). The results indicate that spin-orbit coupling has a much stronger effect on the
monolayer properties compared to the effects of spin-polarization. In general, the GGA is found to predict a larger lattice
constant and a smaller cohesive energy compared to LDA predictions. We also find a significant compression of the monolayers
compared to the bulk, contradicting the only other published result on a Pu monolayer. The current result supports the existence
of a δ-like surface on α-Pu.
Received 17 October 2001 Published online 6 June 2002 相似文献
15.
Faruque M. Hossain Leigh Sheppard Graeme E. Murch 《Journal of Physics and Chemistry of Solids》2008,69(7):1820-1828
The optical properties of rutile and anatase titanium dioxide (TiO2) are calculated from the imaginary part of the dielectric function using pseudopotential density functional method within its generalized gradient approximation (GGA) and a scissors approximation. The fundamental absorption edges calculated for the unit cell of both rutile and anatase are consistent with experimentally reported results of single crystal rutile and anatase TiO2 and with previous theoretical calculations. A significant optical anisotropy is observed in the anatase structure which holds promise for investigating the band gap modification with better visible-light response and provides a reliable foundation for addressing the effect of impurities on the fundamental absorption edge/band gap of anatase TiO2. Further calculations on the electronic structure and the optical properties of C-, N-, and S-doped anatase TiO2 are performed. The results are analyzed and discussed in terms of optical anisotropy and scissors approximations. 相似文献
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18.
S.Zh. Karazhanov P. Ravindran U. Grossner H. Fjellvåg 《Solid State Communications》2006,139(8):391-396
The electronic structure, band parameters, and optical spectra of wurtzite-type ZnO were studied by first-principles calculations within different approximations of the density functional theory. The local-density approximation underestimates the band gap, the energy levels of the Zn-3d states, the band dispersion, the crystal-field splitting, the spin-orbit interaction, and location of peaks in the optical spectra. The generalized-gradient approximation slightly corrects the discrepancies with the experimental findings and it shows good agreement for the optical spectra with experimental data at energies 10-20 eV for E⊥c. Studies within the local-density approximation with the multiorbital mean-field Hubbard potential show that strong Coulomb correlations are in operation. From effective mass calculations it is found that holes are much heavier and more anisotropic than the conduction-band electrons in ZnO. 相似文献
19.
Magnetic properties,electronic structure,and optical properties of the filled skutterudite BaFe4Sb12
The magnetic properties, electronic structure, and optical properties of the filled skutterudite BaFe4Sb12 are calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) plus local orbital method. It is found that the local spin density approximation (LSDA) method appears more accurate than the generalized gradient approximation (GGA) method in calculating the electronic structures and optical properties of this compound. Furthermore, our calculated lattice constant and spin magnetic moments with the LSDA method are in overall better agreement with experiment. In contrast with recent experiment, our calculations are in good agreement with experimental reflectivity spectra and optical conductivity spectrum. 相似文献
20.
EuAlO3 (EAO) is synthesized by the sol–gel process. The Rietveld refinement of the X-ray diffraction data shows that the material has orthorhombic structure with Pbnm space group. The density functional theory calculations are initiated with the experimental lattice parameters. The full potential linearized augmented plane wave method and projector augmented wave method are used to investigate the ground state properties of EAO. An indirect band gap of 1.8 eV is observed with the valence band maximum at the Γ point and the conduction band minimum at the R point. The X-ray photoemission spectroscopy (XPS) spectra of EAO are obtained in the energy window of 0–1000 eV. Using the electronic density of states, the valence band (VB) spectrum of EAO is generated and compared with the observed VB-XPS spectrum. The optical dielectric constant and the refractive index of the material are calculated for the photon energy radiation. The optical properties show a considerable anisotropy in the material. The Born effective charge of various elements and the dielectric tensor of EAO have been calculated. 相似文献