Electronic Structure and Optical Properties of La-Doped SrTiO3 and Sr2TiO4 by Density Function Theory

The effect of La doping on the electronic structure and optical properties of SrTiO₃ and Sr₂TiO₄ is investigated by the first-principles calculation of plane wave ultrasoft pseudopotential based on the density function theory (DFT). The calculated results reveal that the electron doping in the case of Sr_0.875La_0.125TiO₃ and Sr_1.875La_0.125TiO₄ can be described within the rigid band model. The La³⁺ ions fully acts as electron donors in Sr_0.875La_0.125TiO₃ and Sr_1.875La_0.125TiO₄ systems and the Fermi level shifts further into the conduction bands (CBs) for Sr_1.875La_0.125TiO₄ compared to Sr_0.875La_0.125TiO₃. The two systems exhibit n-type degenerate semiconductor features. At the same time, the density of states (DOS) of the two systems shift towards low energies and the optical band gaps are broadened. The Sr_1.875La_0.125TiO₄ is highly transparent with the transmittance about 90% in the visible range, which is larger than that of Sr_0.875La_0.125TiO₃(85%). The wide band gap, small transition probability and weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the optical transparency of the films...     

Electronic Structure and Optical Properties of Semiconducting Orthorhombic BaSi2

Full potential linearized augmented plane wave （FPLAPW） method calculations are carried out for semiconducting orthorhombic BaSi2. The optical properties and the origin of the different optical transitions are investigated. Our calculated band gap of 1.0918eV is indirect, which is in good agreement with the experimental result. The bonds between Ba and Si are considered to be electrovalent bond. The anlsotropy in the imaginary part ε2（w） and real part εl（w） of the optical dielectric tensor are analysed. The contributions of various transition peaks are explained from the imagnary part of the dielectric function.     

Electronic structure calculations of transparent conductor Cd3TeO6: Optical properties and the effect of In-substitution

The electronic structure of Cd₃TeO₆ has been studied in the terms of first-principles calculations based on the density functional theory in order to investigate their optical properties and In-substitution effects. It was found that the highly dispersed bottom of the conduction band formed from Cd-s orbitals is the origin of the high transparency and conductivity. Cd₃TeO₆ exhibited optical anisotropy in its main crystal axes, and the c-axis showed the most suitable crystal growth direction for obtaining a wide transparent region. A pronounced shift of the absorption edge was effectively observed by the In-substitution, reflecting the domination of the In-5s level in the conduction band near the Fermi level.     

Structural, Elastic and Electronic Properties of ReO2

Structural, elastic and electronic properties of ReO₂ are investigated by first-principles calculations based on density functional theory. The ground stateof ReO₂ has an orthorhombic symmetry which belongs to space group Pbcn with a=4.7868Å b=5.5736Å, and c=4.5322Å. The calculated bulk moduli are 322GPa, 353GPa, and 345GPa for orthorhombic, tetragonal, and monoclinic ReO₂, respectively, indicating that ReO₂ has a strong incompressibility. ReO₂ is a metal ductile solid and presents large elastic anisotropy. The obtained Debye temperatures are 850K for orthorhombic, 785K for tetragonal, and 791K for monoclinic ReO₂.     

Electronic Structure of Si1-xⅣx/Si Superlattices on Si （001）

We have preformed systematical ab initio studies of the structural and electronic properties of short-period Si1-xⅣx/Si （x = 0.125, 0.25, 0.5, Ⅳ=Ge, Sn） superlattices （SLs） grown along the [001] direction on bulk Si. The present calculations reveal that the Si0.875Ge0.125/Si, Si0.75Ge0.25/Si and Si0.875Sn0.125/Si are the F-point direct bandgap semiconductors. The technological importance lies in the expectation that the direct gap Si1-xⅣx/Si SLs may be used as components in integrated optoelectronic devices, in conjunction with the already well-established and highly advanced silicon technology.     

Geometric and Electronic Properties of SrCoO2.5: An LSDA+U Study

The geometric and electronic properties of SrCoO_2.5 have been studied using the local-spin density approximation together with the Hubbard method. The geometric optimization shows that the energy of a unit supercell for SrCoO_2.5 with the space group Pnma is at least 1.37eV lower than the others, so we infer that the Pnma structure is the ground state of SrCoO_2.5 at low temperature. The electronic band structure calculations demonstrate that the paramagnetic ordering SrCoO_2.5 at high temperature has the character of an indirect band gap semi-conductor, while the antiferromagnetic ordering SrCoO_2.5 at low temperature has the character of a conductor. The magnetism calculation shows that the magnetic moment of Co is 2.96μ_B, comparable with the experimental measurement at the liquid nitrogen temperature, i.e. 3.30±0.5μ_B.     

Mechanical Properties and Electronic Structures of Cotunnite TiO2

Based on the first-principles plane-wave basis pseudopotential calculations, we investigate mechanical properties and electronic structures of the hardest known oxide, cotunnite TiO2. The calculated results show that cotunnite TiO2 has the highest bulk modulus （348 GPa） and hardness （32 GPa） among the high-pressure phases of TiO2, but its mechanical properties are not superior to those of c-BN. Moreover, the high hardness of cotunnite TiO2 can be understood from both the dense crystal structure （high valence electron density and short bond lengths） and the unusual mixtures of covalent and ionic bonding of Ti-O.     

First-Principles Study of Structural and Electronic Properties of Layered B2CN Crystals

Based on the hexagonal BN structure, six possible layered B~ CN structures are constructed. Their total energies, lattice constants as well as electronic properties are calculated using the ab initio pseudopotential density functional method within the local density approximation. The calculated results show that the B2 CN-V configuration with AA stacking sequence is the most stable among the six B2CN layered structures. The characteristics of electronic structures indicate that the B2 CN-V shows metallicity, which mainly comes from -B1-C-B1-C- chains.     

Electronic structure calculations for BaSxSe1−x alloys

A series of first principles calculations have been carried out to study structural, electronic properties of BaS_xSe_1−x alloys. We have used the local density as well as the generalized gradient approximations for the exchange-correlation potential. The structural properties of these materials, in particular the composition dependence to the lattice constant and bulk modulus, are found to be linear. It is also found linear relationship between theoretical band gaps and 1/a² (where a is lattice constant).     

Coupling of Magnetization and Structural Distortions in Multiferroic BiFeO3： an Ab Initio Density Functional Theory Study

The coupling between magnetism and structural distortions in BiFeO3 （BFO） is investigated using density functional theory by considering the spin-orbit effect. Computational results show that the resulting magnetization M is rotated by reversal of sense of rotation of the oxygen octahedra in the double cell. The resulting magnetization is determined by the antiferrodistortive （AFD） distortions and ferroelectric （FE） displacements. This work clarifies the previous view that magnetism is only coupled with, and determined by, FE displacements. The excellent ferroelectricity is attributed significantly to the anomaly of Born effective charge of Bi, which is caused by the stereochemically active long pair of Bi 6s.     

First-principles prediction of coexistence of magnetism and ferroelectricity in rhombohedral Bi2FeTiO6

First principles calculations based on the density functional theory within the local spin density approximation plus U(LSDA + U) scheme, show rhombohedral Bi₂FeTiO₆ is a potential multiferroic in which the magnetism and ferroelectricity coexist. A ferromagnetic configuration with magnetic moment of 4μB per formula unit has been reported with respect to the minimum total energy. Spontaneous polarization of 27.3 μC/cm², caused mainly by the ferroelectric distortions of Ti, was evaluated using the berry phase approach in the modern theory of polarization. The Bi-6s stereochemical activity of long-pair and the ‘d⁰-ness’ criterion in off-centring of Ti were coexisting in the predicted new system. In view of the oxidation state of Bi³⁺, Fe²⁺, Ti⁴⁺, and O²⁻ from the orbital-resolved density of states of the Bi-6p, Fe-3d, Ti-3d, and O-2p states, the valence state of Bi₂FeTiO₆ in the rhombohedral phase was found to be Bi³⁺₂Fe²⁺Ti⁴⁺O₆.     

First-principles calculations of the electronic and optical properties of In6S7 compound

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.     

Ab Initio Study of Structural and Electronic Properties of Hexagonal BC2N

We investigate hexagonal BC2N in graphite unit cells using the first-principles method and calculate the total energies, lattice parameters, and electronic band structures after full relaxation. It is shown that stable hexagonal BC2N should be stacked sequentially with one graphite layer and one h-BN layer. The density of states indicates that this structure should have metallicity.     

First-Principles Calculations for Thermodynamic Properties of Perovskite-Type Superconductor MgCNi3

The ground state properties and equation of state of the non-oxide perovstdte-type superconductor MgCNi3 are investigated by first-principles calculations based on the plane-wave basis set with the local density approximation （LDA） as well as the generalized gradient approximation （GGA） for exchange and correlation, which agree well with both theoretical calculations and experiments. Some thermodynamic properties including the heat capacity, the thermal expansion coefficient and the Griineisen parameter for perovskite structure MgCNi3 are obtained. The dependences of these thermodynamic properties on pressure and temperature are given for the first time.     

First-principles study of electronic structure, chemical bonding, and optical properties of cubic SrHfO3

Electronic structure and optical properties of SrHfO₃ are calculated using the full potential linearized augmented plane wave plus local orbitals method. The calculated equilibrium lattice is in reasonable agreement with the experimental data. From the density of states (DOS) as well as charge density studies, we find that the bonding between Sr and HfO₃ is mainly ionic and that HfO₃ entities bond covalently. The complex dielectric functions are calculated, which are in good agreement with the available experimental results. The effect of the spin-orbit coupling on the optical properties is also investigated and found to be quite small.     

First Principles Study on Electronic Structures of Mn^2＋：CdMoO4 Crystals

Electronic structures of the Mn^2＋ ：CdMoO4 crystal axe studied within the framework of the fully relativistic self-consistent Dirac Slater theory, using a numerically discrete variation （DV-Xα） method. The calculated results indicate that the 3d states of Mn have donor energy level in the forbidden band of CdMoO4 crystal. The O^2- transition energy of O 2p→Mn 3d is 3.12eV under excitation corresponding electronic transition being O^2-＋Mn^2＋→↑hvex=3.12 eV O^-- ＋Mn^＋→↑hvem O^2-＋Mn^2＋. It is predicted that the wavelength of emission should be located in the range of the 500-600nm. Thus the 500-600mm emission bands peaking at 550nm （2.25eV） of CdMoO4 crystal under excitation may be related to the Mn-like dopant ion in CdMoO4 crystal.     

Li- Site and Metal-Site Ion Doping in Phosphate-Olivine LiCoPO4 by First-Principles Calculation

We present a first-principles investigation of the crystal and electronic structure as well as the average insertion voltage of the Li-site （by Na and Cr） and metal-site （by isovalent Ni, Zn, Ca, Mg and Mn and aliovalent Cu, Al, In, Mo and Zr） doped LiCoPO4. The results show that both the Li-site doping and metal-site doping may reduce the volume change of the material during Li extraction/reinsertion process. The metal doped at Li-site will block the path of Li ion diffusion. The doping by aliovalent transition metals will introduce defect levels in the energy band. It could influence the conductivity insertion voltage.     

First-Principles Calculation of Electronic Structure and Optical Properties of Sb-Doped ZnO

The geometric structure, electronic structure, optical properties and the formation energy of Sb-doped ZnO with the wurtzite structure are investigated using the first-principles ultra-soft pseudo-potential approach of plane wave based upon the density functional theory. The calculated results indicate that the volume of ZnO doped with Sb becomes larger, and the doping system yields the lowest formation energy of Sb on the interstitial site and the oxygen site. Furthermore, Sb dopant first occupies the octahedral oxygen sites of the wurtzite structure. It is found that Sb substituting on oxygen site behaves as a deep acceptor and shows the p-type degenerate semiconductor character. After doping, the electron density difference demonstrates the considerable electron charge density redistribution, which induces the effect of Sb-doped ZnO to increase the charge overlap between atoms. The density of states move towards lower energy and the optical band gap is broadened. Our culated results are in agreement with other experimental results and could make more precise monitoring and controlling possible during the growth of ZnO p-type materials.     

First-principle calculations of structural, electronic and optical properties of BaTiO3 and BaZrO3 under hydrostatic pressure

A theoretical study of structural, electronic and optical properties of cubic BaTiO₃ and BaZrO₃ perovskites is presented, using the full-potential linear augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. In this approach the local density approximation (LDA) is used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus, its pressure derivative, band structure, density of states, pressure coefficients of energy gaps and refractive indices. The results are compared with previous calculations and experimental data.     

The electronic structure and magnetic properties of metallic antiferromagnetic Co[(CH3PO3)(H2O)] studied by first-principles calculations

The electronic structure, the metallic and magnetic properties of metal phosphonate Co[(CH₃PO₃)(H₂O)] have been studied by first-principles calculations, which were based on the density-functional theory (DFT) and the full potential linearized augmented plane wave (FPLAPW) method. The total energy, the spin magnetic moments and the density of the states (DOS) were all calculated. The calculations reveal that the compound Co[(CH₃PO₃)(H₂O)] has a stable metallic antiferromagnetic (AFM) ground state and a half-metallic ferromagnetic (FM) metastable state. Based on the spin distribution obtained from calculations, it is found that the spin magnetic moment of the compound is mainly from the Co²⁺, with some small contributions from the oxygen, carbon and phosphorus atoms, and the spin magnetic moment per molecule is 5.000μ_B, which is in good agreement with the experimental results.