Structural,electronic, optical and bonding properties of strontianite,SrCO3: First-principles calculations

The first-principles calculations are performed within the density functional theory to investigate the crystal structure, energy band structure, density of states, optical properties, and bonding properties of strontianite. The optimized structure parameters and bonding results with the generalized gradient approximation (GGA) functional and the localized density approximation (LDA) functional are in good agreement with the earlier experimental data. The band structure, density of states and chemical bonding of strontianite have been calculated and analyzed. The indirect band gap of strontianite is estimated to be ~4.45 eV (GGA) or ~4.24 eV (LDA). The absorption, reflectivity, refractive index and extinction coefficient have been calculated using the imaginary part of the dielectric function. The calculated results of the optical properties show that strontianite has an optical anisotropy along [100] (or [010]) and [010] polarization directions of incoming light. Furthermore, the calculated results of the density of states and Mulliken population indicate that the interactions among atoms are both ionic and covalent bonding in strontianite.     

LiGaX2(X=S,Se, Te)的电子结构,光学和弹性性质的第一性原理计算

采用基于第一性原理的密度泛函理论赝势平面波方法,对LiGaX₂(X=S, Se, Te)的能带结构、态密度、光学以及弹性性质进行了理论计算. 能带结构计算表明LiGaS₂ 的禁带宽度为4.146 eV, LiGaSe₂ 的禁带宽度为3.301 eV, LiGaTe₂ 的禁带宽度为2.306 eV; 其价带主要由Ga-4p 层电子和X- np 层电子的能态密度决定; 同时也对LiGaX< 关键词： 电子结构 光学性质 弹性性质 LGX     

First-principles studies of the electronic structure and optical properties of AgBO<Subscript>3</Subscript> (B=Nb,Ta) in the paraelectric phase

The electronic energy-band structure, density of states (DOS), and optical properties of AgBO₃ in the paraelectric cubic phase have been studied by using density functional theory within the local density approximation for exchange-correlation for the first time. The band structure shows a band gap of 1.533 eV (AgNbO₃)and 1.537 eV (AgTaO₃)at (M-⌈)point in the Brillouin zone. The optical spectra of AgBO₃ in the photon energy range up to 30 eV are investigated under the scissor approximation. The real and imaginary parts of the dielectric function and — thus the optical constants such as reflectivity, absorption coefficient, electron energy-loss function, refractive index, and extinction coefficient — are calculated. We have also made some comparisons with related experimental and theoretical data that is available.      

Theoretical Study of the Structural,Electronic, Chemical Bonding and Optical Properties of the A2<Subscript>1</Subscript><Emphasis Type="Italic">am</Emphasis> Orthorhombic SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript>

The structural parameters, density of states, electronic band structure, charge density, and optical properties of orthorhombic SrBi₂Ta₂O₉ have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principle density functional theory (DFT). The calculated structural parameters were in agreement with the previous theoretical and experimental data. The band structure showed an indirect (S to Γ) band gap with 2.071 eV. The chemical bonding along with population analysis has been studied. The complex dielectric function, refractive index, and extinction coefficient were calculated to understand the optical properties of this compound, which showed an optical anisotropy in the components of polarization directions (100), (010), and (001).     

UO2的电子结构及光学性质的第一性原理研究

采用局域自旋密度近似 (LSDA)和有效库仑相关能 (U) 方法研究了UO₂的晶格参数、能带结构和光学常数. 计算得到的UO₂晶体的晶格常数为5.40 ?,带隙宽度为1.82 eV,正确预测了UO₂的反铁磁性半导体基态性质. 能带结构和介电函数的分析结果表明,铀的6d电子在晶体场中发生劈裂形成两个能级,与实验结果较为符合.     

Structural, electronic and optical properties of orthorhombic distorted perovskite TbMnO3

This paper calculates the structural parameters, electronic and optical properties of orthorhombic distorted perovskite-type TbMnO3 by first principles using density functional theory within the generalised gradient approximation. The calculated equilibrium lattice constants are in a reasonable agreement with theoretical and experimental data. The energy band structure, density of states and partial density of states of elements are obtained. Band structures show that TbMnO3 is an indirect band gap between the O 2p states and Mn 3d states, and the band gap is of 0.48 eV agreeing with experimental result. Furthermore, the optical properties, including the dielectric function, absorption coefficient, optical reflectivity, refractive index and energy loss spectrum are calculated and analysed, showing that the TbMnO3 is a promising dielectric material.     

Sc2O3电子结构和光学性质的第一性原理研究

本文基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,研究了Sc2O3的电子结构、态密度和光学性质. 计算结果表明：Sc2O3是一种直接带隙半导体,其能带宽度为3.79eV,价带顶部主要由O的2p和Sc的3p3d杂化而成,导带主要由Sc的3d和O的2p构成. 同时,文中也分析了Sc2O3的介电函数、折射率、光电导率和吸收谱等光学性质. 计算得到静态介电常数 ,折射率n0=1.25,在紫外区有较大的吸收系数.     

Electronic and optical properties of defect chalcopyrite HgAl2Se4

The structural, electronic and optical properties of HgAl₂Se₄ are investigated using the full potential linear augmented plane wave method based on density functional theory. The calculated structural parameters using LDA are in excellent agreement with the available experimental result. The obtained energy band gap (2.24 eV) using EV-GGA approximation is in excellent agreement with experimental data (2.20 eV). Variation in the energy band gap as a function of the unit cell lattice parameter has been studied. The optical properties show a considerable anisotropy, which makes this compound very useful for various linear–nonlinear optical devices.     

Structural,elastic, electronic and optical properties of the cubic perovskites CaXO3 (X=Hf and Sn)

The structural, elastic, electronic and optical properties of CaXO₃ compounds with the cubic perovskites structure have been investigated, by employing a first principles method, using the plane wave pseudo potential calculations (PP-PW), based on the density functional theory (DFT), within the local density approximation (LDA). The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk, shear and Young’s moduli for ideal monocrystalline and for polycrystalline CaXO₃ aggregates which we have classified as ductile in nature. Band structures reveal that these compounds are indirect energy band gap (R-G) semiconductors; the analysis of the site and momentum projected densities, valence charge density bond length, bond population and Milliken charges, shows that bonding is of covalent–ionic nature. We have found that the elastic constants C₁₁, C₁₂, C₄₄ are in good correlation with the bonding properties. The optical constants, including the dielectric function, optical reflectivity, refractive index and electron energy loss, are calculated for radiation up to 20 eV.     

First principles study of electronic structure and optical properties of CaTiO3

The electronic-energy band structure, site and angular momentum decomposed density of states (DOS) and charge-density contours of perovskite CaTiO ₃ are calculated by the first principles tight-binding linear muffin-tin orbitals method with atomic sphere approximation using density functional theory in its local density approximation. The calculated band structure shows an indirect (R-Γ) band gap of 1.5 eV. The total DOS as well as the partial density of states (PDOS) are compared with the experimental photoemission spectra. The calculated DOS are in reasonable agreement with the experimental energy spectra and the features in the spectra are interpreted by a comparison of the spectra with the PDOS. The origin of the various experimentally observed bands have been explained. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Ca and TiO ₃ is mainly ionic and that the TiO ₃ entities bond covalently. Using the projected DOS and band structure we have analyzed the interband contribution to the optical properties of CaTiO ₃ . The real and imaginary parts of the dielectric function and hence the optical constants such as refractive index and extinction coefficient are calculated. The calculated spectra are compared with the experimental results for CaTiO ₃ and are found to be in good agreement with the experimental results. The effective number of electrons per unit cell participating in the interband transitions are calculated. The role of band structure calculation as regards the optical properties of CaTiO ₃ is discussed. Received 1 February 2000 and Received in final form 21 July 2000     

First-principles study on the electronic and optical properties of BiFeO3

The structural, electronic, and optical properties of multiferroic bismuth ferrite (BiFeO₃) are investigated using density functional theory within generalized gradient approximation (GGA). The calculated lattice parameters are in good agreement with the experimental data. The electronic structure shows that BiFeO₃ has an indirect (very close to direct) band gap of 1.06 eV. The complex dielectric function, absorption spectra, refractive index, extinction coefficient, energy-loss spectrum and reflectivity are calculated, and the results are compared with the available experimental data. Finally, the optical properties of BiFeO₃ are discussed based on the band structure calculations.     

Ab initio calculations study of the electronic, optical and thermodynamic properties of NaMgH3, for hydrogen storage

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.     

First principles study of the electronic and optical properties of SbTaO4

The electronic density of states (DOS), band structure and optical properties of orthorhombic SbTaO₄ are studied by first principles full potential-linearized augmented plane wave (FP-LAPW) method. The calculation is done in the framework of density functional theory with the exchange and correlation effects treated using generalized gradient approximation (GGA). We find an indirect band gap of 1.9 eV at the R→Γ symmetry direction of the Brillouin zone in SbTaO₄. It is observed that there is a strong hybridization between Ta-5d and O-2p electronic states which is responsible for the electronic properties of the system. Using the projected DOS and band structure we have analyzed the interband contribution to the optical properties of SbTaO₄. The real and imaginary parts of the dielectric function of SbTaO₄ are calculated, which correspond to electronic transitions from the valence band to the conduction band. The band gap obtained is in close agreement with the experimental data.     

First-principles study of the structural, elastic, electronic and optical properties of the monoclinic BiScO3

The structural, elastic, electronic and optical properties of the monoclinic BiScO₃ are investigated in the framework of the density functional theory. The calculated structural parameters are in agreement with the experimental values. Moreover, the structural stability of BiScO₃ system has been confirmed by the calculated elastic constants. The band structure, density of states, charge transfers and bond populations are also given. The results indicate that BiScO₃ has a direct band gap of 3.36 eV between the occupied O 2p states and unoccupied Bi 6p states, and its bonding behavior is a combination of covalent and ionic nature. Finally, the absorption spectrum, refractive index, extinction coefficient, reflectivity, energy-loss function and dielectric function of the monoclinic BiScO₃ are calculated. In addition, the variation of the static dielectric constants ε₁(0) as a function of pressure for BiScO₃ is also discussed.     

Electronic structure and optical properties of Sb2S3 crystal

The electronic and optical properties of Sb₂S₃ are studied using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in Wien2k. In this approach, the alternative form of the generalized gradient approximation (GGA) proposed by Engel and Vosko (EV-GGA) was used for the exchange correlation potential. The calculated band structure shows a direct band gap. The contribution of different bands was analyzed from total and partial density of states curves. Moreover, the optical properties, including the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum are all obtained and analyzed in detail.     

First-principles calculations of structural, electronic, optical and elastic properties of magnesite MgCO3 and calcite CaCO3

Detailed ab initio calculations of the structural, electronic, optical and elastic properties of two crystals - magnesite (MgCO₃) and calcite (CaCO₃) - are reported in the present paper. Both compounds are important natural minerals, playing an important role in the carbon dioxide cycling. The optimized crystal structures, band gaps, density of states diagrams, elastic constants, optical absorption spectra and refractive indexes dependence on the wavelength all have been calculated and compared, when available, with literature data. Both crystals are indirect band compounds, with calculated band gaps of 5.08 eV for MgCO₃ and 5.023 eV for CaCO₃. Both values are underestimated by approximately 1.0 eV with respect to the experimental data. Although both crystals have the same structure, substitution of Mg by Ca ions leads to certain differences, which manifest themselves in noticeable change in the electronic bands profiles and widths, shape of the calculated absorption spectra, and values of the elastic constants. Response of both crystals to the applied hydrostatic pressure was analyzed in the pressure range of phase stability, variations of the lattice parameters and characteristic interionic distances were considered. The obtained dependencies of lattice constants and calculated band gap on pressure can be used for prediction of properties of these two hosts at elevated pressures that occur in the Earth's mantle.     

The electronic structure,electronic charge density and optical properties of the diamond-like semiconductor Ag2ZnSiS4

The electronic structure, electronic charge density and optical properties of the diamond-like semiconductor Ag₂ZnSiS₄ compound with the monoclinic structure have been investigated using a full-relativistic version of the full-potential augmented plane-wave method based on the density functional theory, within local density approximation (LDA), generalized gradient approximation (GGA), Engel–Vosko GGA (EVGGA) and modified Becke Johnson (mBJ) potential. Band structures divulge that this compound is a direct energy band gap semiconductor. The obtained energy band gap value using mBJ is larger than those obtained within LDA, GGA and EVGGA. There is a strong hybridization between Si-s and S-s/p, Si-p and Zn-s, Ag-s/p and Zn-s, and Ag-s and Ag-p states. The analysis of the site and momentum-projected densities shows that the bonding possesses covalent nature. The dielectric optical properties were also calculated and discussed in detail.     

Electronic structure and optical properties of CdWO4 with oxygen vacancy studied from first principles

The electronic structures, dielectric functions and absorption coefficient of both perfect CdWO₄ crystal (CWO) and the CWO crystal containing oxygen vacancy (CWO: V _O) have been studied using the CASTEP code with the lattice structure optimized. The calculated total density of states (TDOS) of CWO: V _O indicates that the oxygen vacancy would introduce a new electronic state within the band gap compared with that of perfect CWO. The dielectric functions are calculated since the imaginary part of the dielectric function can reduce the optical absorption of a certain crystal, and then the absorption coefficient is calculated. The calculated absorption spectra show that CWO: V _O exhibits two absorption bands in the ultraviolet and visible region, peaking at about 3.0 eV (413 nm) and 3.5 eV (354 nm), respectively, which are in agreement with the experimental results showing that the yellow CWO has two optical absorption bands in this region peaking at around 350 nm and 400 nm respectively. It can be concluded that oxygen vacancy causes these two absorption bands. The calculations also indicate that the optical properties of CWO exhibit anisotropy, and can be explained by the anisotropy of the crystal lattice.     

First principles study of structural, elastic, electronic and optical properties of the cubic perovskite BaHfO3

First principles study of structural, elastic, electronic and optical properties of the cubic perovskite-type BaHfO₃ has been reported using the pseudo-potential plane wave method within the local density approximation. The calculated equilibrium lattice is in a reasonable agreement with the available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. Band structures show that BaHfO₃ is a direct band gap between the occupied O 2p and unoccupied Hf d states. The variation of the gap versus pressure is well fitted to a quadratic function. Furthermore, in order to understand the optical properties of BaHfO₃, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. We have found that O 2p states and Hf 5d states play a major role in the optical transitions as initial and final states, respectively. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of BaHfO₃ compound, and it still awaits experimental confirmation.