Static structure factor and electronic transport properties of liquid rubidium from a first principles pseudopotential calculation

A first principles nonlocal pseudopotential calculation is used to obtain the ion-ion potential for liquid rubidium of 45°C. This is then used in a Monte Carlo simulation to determine the liquid structure S(q) and transport properties. It is found that the accuracy of the S(q), in the low q-region, is crucial to the calculation of electronic transport properties.     

Infrared reflectance spectrum of BN calculated from first principles

Using the linear response theory, vibrational and dielectric properties are calculated for c-BN, w-BN and h-BN. Calculations of the zone-center optical-mode frequencies (including LO-TO splittings) are reported. All optic modes are identified and excellent agreement is found between the theory and experimental results. The static dielectric tensor is decomposed into contributions arising from individual infrared-active phonon modes. It is found that all the structures have a smaller lattice dielectric constants than those of the electronic contributions. Finally, the infrared reflectance spectrums are presented. Our theoretical results indicate that w-BN shows a similar reflectivity spectrum as c-BN. It is difficult to tell apart the wurtzite structure from the zinc blende phase by IR spectroscopy.     

Electronic structure and optical properties of TaC from the first principles calculation

The electronic and optical properties of tantalum carbide TaC have been calculated using the full-potential linearized augmented-plane-wave method within the local density approximation scheme for the exchange-correlation potential. We find that the optical spectra can be extremely sensitive to the Brillouin zone sampling. The influence of relativistic effects on the dielectric function is investigated. It is shown that the scalar-relativistic correction is much more important than spin-orbit coupling. Our results are found to be in good agreement with the available experimental data. The determinant role of a band structure computation with respect to the analysis of optical properties is discussed.     

Electronic structure and magnetic properties of rare-earth perovskite gallates from first principles

The density functional calculation is performed for centrosymmetric(La–Pm) GaO_3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA+U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U = 0.478 Ry on the magnetic phase stability and the densities of states. LSDA+U calculation shows that the ferromagnetic(FM) state of RGaO_3 is energetically more favorable than the anti-ferromagnetic(AFM) one, except for LaGaO_3 where the NM state is the lowest in energy. The energy band gaps of RGaO_3 are found to be in the range of 3.8–4.0 eV, indicating the semiconductor character with a large gap.     

The structural, elastic and thermodynamical properties of zinc-blend structure InN from first principles

A theoretical study of the structural, elastic and thermodynamic properties of the cubic zinc-blende (ZB) structure InN are presented in this paper by performing first principles calculations within local density approximation. The values of lattice constant, bulk modulus and its pressure derivatives and elastic constants are in excellent agreement with the available experimental data and other theoretical results. It is found that the ZB structure InN should be unstable above 20 GPa mechanically. The pressure and temperature dependencies of the bulk modulus, the heat capacity and the thermal expansion coefficient and the entropy S, as well as the Grüneisen parameter are obtained by the quasi-harmonic Debye model in the ranges of 0-1500 K and 0-25 GPa.     

Superconducting properties of MgB2 from first principles

Solid MgB(2) has rather interesting and technologically important properties, such as a very high superconducting transition temperature. Focusing on this compound, we report the first nontrivial application of a novel density-functional-type theory for superconductors, recently proposed by the authors. Without invoking any adjustable parameters, we obtain the transition temperature, the gaps, and the specific heat of MgB(2) in very good agreement with experiment. Moreover, our calculations show how the Coulomb interaction acts differently on sigma and pi states, thereby stabilizing the observed superconducting phase.     

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.     

Electronic structure and optical properties of rutile RuO2 from first principles

The systematic trends of electrionic structure and optical properties of rutile (P42 /mnm) RuO2 have been calculated by using the plane-wave norm-conserving pseudopotential density functional theory (DFT) method within the generalised gradient approximation (GGA) for the exchange-correlation potential.The obtained equilibrium structure parameters are in excellent agreement with the experimental data.The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations.Analysis based on electronic structure and pseudogap reveals that the bonding nature in RuO2 is a combination of covalent,ionic and metallic bonds.Based on a Kramers-Kronig analysis of the reflectivity,we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant (ε1 and ε2,respectively) and the refractive index (n);and comparisons have shown that the theoretical results agree well with the experimental data as well.Meanwhile,we have also calculated the absorption coefficient,reflectivity index,electron energy loss function of RuO2 for radiation up to 30 eV.As a result,the predicted reflectivity index is in good agreement with the experimental data at low energies.     

Elastic properties and phonon dispersions of rhenium in hexagonal-close-packed structure under pressure from first principles

The elastic properties of the hexagonal-close-packed (hcp) structure rhenium (Re) and their behavior under pressure are investigated using the local density approximation (LDA) and the generalized gradient approximation (GGA). The obtained high pressure elastic constants are well consistent with previous theoretical date, while large discrepancies are found between theory and the high pressure experiments. The calculated isothermal bulk modulus B₀ (376 GPa for GGA and 389 GPa for LDA) and its initial pressure derivative (4.52 for LDA and 4.58 for GGA) compare favorably with the experimental values. Moreover, it is found that the value of c/a, B/G, Poisson's ratio, and B_c/B_a are virtually independent of pressure. We also performed calculation for phonon dispersions at high pressure. GGA in our calculation exhibits a same trend as the high pressure experimental curve.     

Theoretical study of superconducting state parameters of binary metallic glasses by a pseudopotential method

The theoretical investigations of the superconducting state parameters (SSP) viz. electron–phonon coupling strength λ, Coulomb pseudopotential μ¹, transition temperature T_C, isotope effect exponent α and effective interaction strength N₀V of binary metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that λ and T_C are quite sensitive to the selection of the local field correction functions in comparisons with μ¹, α and N₀V. The T_C obtained from H-local field correction function is found in qualitative agreement with available experimental data and show linear nature with the concentration (C). A linear T_C equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other results for the experimental data. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the metallic glasses.     

Electronic band structure of partially inverse spinel MgIn2S4 as calculated by the semiempirical pseudopotential method

The electronic band structure of the partially inverse spinel MgIn₂S₄ has been calculated on the symmetry lines ΓΛL, ΓΔX and ΓΣK by the semiempirical pseudopotential method. The general features of the band structure of MgIn₂S₄ are quite similar to those of the normal spinel CdIn₂S₄. The conduction band minimum is located at Γ and the valence band maximum is along the Σ line. The indirect energy gap (Γ_1cΣ_4v) is 2.50 eV. The effects of magnesium vacancy and variations in the cation distribution and in the parameter u are examined and shown to be small.     

Calculation of elastic and thermal properties of alkali metals by the pseudopotential method

The elastic and thermal properties of alkali metals are analyzed from the viewpoint of effective ion-ion interaction in rectilinear space. Consideration is given to the approximation of pair interaction between ions. The atomic-interaction potential is calculated on the basis of the pseudopotential method. Numerical calculations are made of the elastic constants, the second and fourth moments of the frequency spectrum, the temperature dependence of the Debye temperature, the specific heat, and the vibrational free energy of Na, K, Rb, and Cs. The calculations are in good agreement with the experimental values. The influence of exchange-correlation effects on the given properties is discussed. The results obtained indicate that the pseudopotential method may be successfully used for the calculation of the thermodynamic properties of metals by a traditional scheme, restricting consideration to the first two coordination spheres.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 25–33, February, 1979.     

Investigation of the interatomic interaction and structure in liquid metals by the pseudopotential method

The calculation of the interatomic interaction by the pseudopotential method with different models for the form factors has been considered, and the effect of the kind of screening of the electron gas on the form of the potential has been investigated. The potentials of the pair interaction which were calculated have been used to solve the Bogolyubov-Born-Green and the Percus-Yevick integral equations for the radial distribution function. Questions about the applicability of this method for computing the structure and thermodynamic properties of liquid metals are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 44–49, November, 1979.     

Electronic structure and related properties of ferrocyanide ion calculated by the SCF Xα-scattered wave method

The SCF-XαSW method is used to calculate the electronic structure of the ferrocyanide ion. Optical transitions and X-ray photoelectron emission are obtained from the energy level scheme and compared with experimental results. The charge density in the Fe nucleus is also computed and the result is correlated with isomer shift measurements made on this and other Fe complexes for which theoretical calculations have been performed.     

Derivation from first principles of the infrared structure of quantum electrodynamics

It is shown how a contribution to the action from a surface at spatial infinity determines the infrared structure of quantum electrodynamics.     

Static dielectric properties of carbon nanotubes from first principles

We characterize the response of isolated single-wall (SWNT) and multiwall (MWNT) carbon nanotubes and nanotube bundles to static electric fields using first-principles calculations and density-functional theory. The longitudinal polarizability of SWNTs scales as the inverse square of the band gap, while in MWNTs and bundles it is given by the sum of the polarizabilities of the constituent tubes. The transverse polarizability of SWNTs is insensitive to band gaps and chiralities and is proportional to the square of the effective radius; in MWNTs, the outer layers dominate the response. The transverse response is intermediate between metallic and insulating, and a simple electrostatic model based on a scale-invariance relation captures accurately the first-principles results. The dielectric response of nonchiral SWNTs in both directions remains linear up to very high values of applied field.     

第一性原理研究缺陷对高压下LiF的电子结构和光学性质的影响

基于密度泛函理论下的平面波超软赝势方法,本文计算了102 GPa压力下LiF理想和含空位（Li-1 、F+1）晶体的电子结构和光学性质.结果表明:102 GPa压力下理想LiF晶体有良好的透明性;高压下Li-1及F+1两种空位的存在不影响LiF的光学透明性.分析其原因：LiF是一种带隙很宽的离子晶体,电子发生跃迁需要较高的能量; LiF中F元素的电负性很大,Li的电负性却很小,二者结合的Li-F键键能很高.另外本文还计算了102 GPa压力下理想LiF晶体及Li-1 、F+1两种空位分别存在时的反射、折射率、介电函数和光损失函数等一些光学性质,并将理想和含空位的做了比较,结果表明：102 GPa压力下空位的存在对LiF在可见光范围内这些光学性质都不产生影响,但由于F+1空位的存在使LiF晶体对光的吸收发生了红移现象.