The nature of the electronic states and photoelectron spectra of oxyanion crystals

The densities of states, atomic charges, and partial components were calculated by the B3LYP method for lithium, sodium, and potassium nitrites, nitrates, chlorates, perchlorates, sulfites, and sulfates using a localized basis of atomic orbitals and CRYSTAL06 software. The calculated densities of states N(E) are in good agreement with the experimental photoelectron spectrum (UPS). The crystallographically nonequivalent metal and oxygen atoms are in different charged states, which leads to a splitting of the N(E) bands.     

Electronic structure of carbon nanotubes with copper core

The electronic structure of copper-intercalated carbon nanotubes has been studied by quantum-chemical methods. The total and partial densities of states of nanotubes have been calculated by the linear augmented-cylindrical-wave method. The armchair (5,5) nanotubes with one, two, three, and four copper atoms per unit cell have been calculated The introduction of the metal is accompanied by a sharp increase in the density of states at the Fermi level of the nanowire, which determines the concentration of free electrons involved in charge transfer in the nanotube. The 3d electrons of the metal and the carbon shell are nearly equally involved in electron transport in intercalated wires.     

Band structure and electronic properties of lithium azide (LiN3)

Ab initio Hartree–Fock band structure and molecular calculations have been performed to study the electronic structure of LiN₃ in a monoclinic C 2/m crystal structure. The total energy, band structure, density of states, and charge densities are computed. The calculated lattice energy (energy to separate the ions infinitely apart) of 8.6 eV agrees very well with 8.45 eV deduced from Madelung and London polarizability energies. The calculated split of the N 1s core bands of 5.0 eV compares favorably with the experimental X-ray photoelectron value of 4.4 eV. This good agreement is not contributed to crystalline environment effects as proposed in earlier MO studies of N where the best values obtained were 5.1, 5.8, and 6.3 eV, but to the quality of the nitrogen core basis set. The calculated valence density of states supports one of two competing interpretations that peak III observed in the X-ray photoelectron spectrum arises from contaminations or other extrinsic states.     

Electronic structure,optical properties and Compton profiles of Bi2S3 and Bi2Se3

In this paper, we present the Compton profiles of Bi₂S₃ and Bi₂Se₃ using our 20 Ci ¹³⁷Cs Compton spectrometer. To compare our experimental data, we have computed the Compton profiles, energy bands and density of states using linear combination of atomic orbitals with density functional theory (DFT) and Hartree-Fock (HF) scheme. It is seen that hybrid functional involving HF and DFT approximations gives a relatively better agreement with experimental momentum densities than other approximations of DFT. We have also reported the band structure, density of states, valence charge densities, dielectric functions and electron energy loss spectra using full potential linearized augmented plane wave scheme. On the basis of charge densities, Mulliken’s population data and equal-valence-electron-density profiles, Bi₂S₃ is found to be more ionic than Bi₂Se₃. The calculated dielectric functions for the parallel and perpendicular polarizations show a small anisotropic effect. The electron energy loss spectrum for Bi₂Se₃ is found to be in good agreement with the available experimental data.     

Chemical bonding in refractory transition metal compounds with 8, 9, and 10 valence electrons

The chemical bonding in the refractory transition metal compounds TiC, TiN, and VN is investigated by experimental and theoretical techniques. High-precision X-ray diffraction is used to determine the electron densities in these three compounds experimentally. The X-ray structure factors and the respective valence electron densities are used twice, once to understand the chemical bonding and once to relate the experimental charge densities to those obtained from band structure calculations. These calculations, which in general are in very good agreement with experimental data, utilize the linearized augmented plane wave (LAPW) method. Theory and experiment lead to a detailed analysis of the chemical bonding in these compounds with 8, 9, and 10 valence electrons. By decomposition of the theoretical charge density into contributions from different states (energy regions), it was possible to show the strong covalent nonmetal p-metal d interaction, which is otherwise apparent only in TiC, but not in TiN or VN. In the latter two compounds the additional electrons occupy mainly metal d states with t_2g symmetry, so that in the total valence charge densities the most important bonding feature is covered. In addition to covalent interactions all compounds have a metallic bonding contribution as well as a considerable charge transfer from the metal to the nonmetal site. This mixture in chemical bonding accounts for the unusual combination of properties such as ultrahardness, high melting points, and good conductivity.     

The crystal structure and surface energy of NaAlH4: a comparison of DFT methodologies

This paper presents a comparison of the bulk structure, cleavage energies, and local densities of states of solid NaAlH4 calculated using several different density functional theory methodologies. Good agreement is obtained for the bulk crystal structure. Larger differences become apparent for the calculated surface energies and local densities of states. The (001) NaAlH4 surface is clearly identified as the most stable surface, followed by the (112) and (101) surfaces, with the (100) surface being the least stable. We present an analysis of the local density of states of atoms in the exposed NaAlH4 surface.     

Al 掺杂对Mg2Ni 合金的电子结构及贮氢性能的影响

采用基于密度泛函理论(DFT)的平面波赝势(PW-PP)方法, 计算Mg_2-xAl_xNiH₄ (x=0, 0.125, 0.25)合金的晶胞体积、电子态密度、键序、电荷布居、生成焓, 分析原子间成键和结构的稳定性, 研究Al 部分替代Mg 对Mg₂Ni 合金及其氢化物的结构和储氢性能的影响. 结果表明: 随着Al 含量的增加, Mg₂Ni 合金晶胞体积减小, 不利于氢原子进入合金中, 导致合金的储氢容量降低. 在Mg_2-xAl_xNiH₄ (x=0, 0.125, 0.25)中, Mg-H和Al-H相互作用远小于Ni-H的相互作用, 随着Al 含量的增加, 氢化物生成焓减少以及Ni-H的相互作用减弱, 氢化物的结构稳定性降低, Al 部分替代Mg能有效改善Mg₂Ni 合金释氢动力学性能.     

X-ray spectra and electronic structure of several ternary chalcogenides and their solid solutions

The electronic energy structure of substitution solid solutions CuGa(S_xSe_1−x)₂ is studied within wide limits of sulfur concentration x in the onion sublattice. The SK absorption spectrum is calculated for CuGaS₂ in a high-order multiple scattering approximation using the FEFF7 program. For all concentrations x, partial densities of states are calculated in a full multiple scattering approximation by the local coherent potential method. The calculation schemes for the filled and vacant states are employed, which differ in a choice of the crystalline potential. The effect of a vacancy on the SK level on the density of the free Sp states is considered. The theoretical K absorption spectra and densities of states of CuGaS₂ are compared with the experimental X-ray and X-ray photoelectron spectra. The calculated curves are in good agreement with the experiment. It is established that the densities of the S and Se p states change smoothly with varying concentration of anions. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1076–1082, November–December, 1998.     

Chemical bonding interactions in Zr2Al

The electronic structure of Zr₂Al with the Ni₂In-type structure has been calculated by the method of W. Kohn and N. Rostoker (Phys. Rev. 91, 1111 (1954)). The results include densities of states, both total and partial, and resolved according to the angular momentum quantum number, and calculated electron densities presented so as to display directional bonding characteristics of electrons in the valence and conduction regions of energy. It is concluded that: (1) the principal bonding involves aluminum s-type orbitals; (2) the aluminum p-type orbitals are principally nonbonding; and (3) the metallic interactions are principally between zirconium atoms.     

Aromatic amines: a comparison of electron-donor strengths

The electron-donor abilities of ten aminophenyl systems and an additional aminothienyl system are compared using density functional theory calculations. The systems studied here include those with amine nitrogen atoms bearing alkyl or aryl groups and those with amine nitrogen atoms as part of a heterocycle. Their abilities to act as donors in electron-transfer processes are assessed from calculated vertical ionization potentials for the aminobenzenes, which are in good agreement with available experimental data. Their abilities to act as intramolecular pi-electron donors in conjugated systems are inferred from the bond lengths and charge densities calculated for the corresponding 4-aminobenzaldehydes and 4-aminobenzonitriles. The computed (13)C NMR chemical shifts for the 4-aminobenzaldehydes and 4-aminobenzonitriles are in good agreement with published and new experimental data. The chemical shifts correlate well with the computed charge densities and can, to some extent, be used as an experimental probe of pi-donor strength. We find that the electron-transfer-donor strengths do not correlate well with pi-donor strengths: these differences can largely be attributed to steric effects.     

Electronic states in clusters of H forms of zeolites with variation of the Si/Al ratio

Fragments of H forms of zeolites of the faujasite type including up to 12 silicon- and aluminum-oxygen tetrahedrons and having different Si/Al ratios have been calculated in the cluster approximation by the MINDO/3 and CNDO/2 methods. The dependence of the integral and orbital densities of electronic states in the clusters on the aluminum content has been investigated. It has been shown that the profiles of the s- and p-orbital density of states of Al remain practically unchanged as the Si/Al ratio is lowered and that the maxima of the orbital density of states of Si broaden, and new maxima appear at the bottom and top of the valence band. When the acidity of the structural OH groups is lowered, the maxima of the orbital density of states of the H atoms are displaced appreciably only in the deep valence band, while in the upper valence band the positions of the peaks of the s-orbital density of states of the H atoms remain constant. Satisfactory agreement of the calculated orbital densities of states of Si, Al, and O with the corresponding x-ray photoelectron spectra has been obtained. In the deep valence band the data from the MINDO/3 method are better than those from the CNDO/2 method and reproduce the positions of the maxima in the x-ray photoelectron spectra.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 1, pp. 95–102, January–February, 1987.     

Electronic structure,Compton profiles and cohesive properties of Cs-halides

We have reported energy bands, density of states, valence electron charge densities and Compton profiles of CsCl, CsBr and CsI using linear combination of atomic orbitals with Hartree–Fock and density functional theories. We have also computed these properties, except the momentum densities, using full potential linearized augmented plane wave method. The general features of the energy bands and the density of states in these halides are found to be almost similar. To interpret the theoretical data on Compton line shapes, we have also measured the Compton profiles using our 20 Ci ¹³⁷Cs spectrometer. It is seen that the Hartree–Fock calculations give relatively a better agreement with the experimental momentum densities. On the basis of equal-valence-electron-density profiles, a comparison of relative nature of bonding is made which is in agreement with the valence charge densities and atomic charges by means of Mulliken analysis. Using our experimental and theoretical Compton profiles, we have also computed the cohesive energy of the halides.     

Excited state properties of novel p- and n-type organic semiconductors with an anthracene unit

Photoinduced dynamics of novel p- and n-type organic semiconductors with an anthracene unit are theoretically investigated with quantum chemistry methods. The calculated vertical absorption and fluorescence frequencies of them are consistent with the experimental data. The changing tendencies of the dihedral angles between anthracene unit and trifluoromethylphenyl (or thiophene) in the photoinduced dynamics processes (vertical absorption and vertical fluorescence) are examined from the geometries of optimized ground and excited states. To study the influence of the individual units of the derivatives to the excited state properties of the derivatives, the energies and densities of frontier orbital HOMOs and LUMOs of the individual unit and the derivatives are studied in the processes of vertical absorption and fluorescence. The excited state properties of the two derivatives in the processes of vertical absorption and fluorescence are studied with 2D and 3D real space analysis methods, which are employed to study the electron–hole coherence and the excitation delocalization (with transition density matrix method), and charge and energy transfer (with transition and charge difference density method). Overall, the computed results remain in good agreement with the relevant experimental data, and the theoretical results promote deeper understanding to the optical and electronic properties of the semiconductor in the process of photoinduced dynamics.     

New Atom/Functional Group Volume Additivity Data Bases for the Calculation of the Crystal Densities of C-, H-, N-, O-, F-, S-, P-, Cl-, and Br-Containing Compounds

The solid-state density of an energetic material is one of the most important parameters related to performance. With crystal structure data from the Cambridge Structural Database, four new additivity data bases have been determined to provide atom and functional group volumes or densities for the calculation of solid-state densities of organic compounds with the elements C, H, N, O, F, P, S, Cl, and Br. Volumes and densities for 96 atoms/groups were determined from approximately 26,000 crystal structure data. Sets of linear volumes (from observed unit cell volume per molecule data) and nonlinear volumes and linear densities (from observed crystal densities) were determined. The concept of an atom code was also introduced to allow the atoms and their connections to define the types of atoms present in a molecule. This approach lead to 1601 atom codes. With more than 2000 crystal structure data that were not used in the initial parameterizations, average percentage differences between the observed volumes/densities and calculated values ranged from 1.8–2.3%.     

First-Principles Study of Bi-Doping Effects in Hg0.75Cd0.25Te

First-principles calculations based on density functional theory have been performed for exploring the structural and electronic properties of Bi-doped Hg_0.75Cd_0.25Te (MCT), using the state-of-the-art computational method with the Heyd–Scuseria–Ernzerhof (HSE) of hybrid functional to correct the band gap. Structural relaxations, charge densities, electron localization functions (ELFs), density of states (DOSs), band structures, and band decomposed charge density were obtained to reveal the amphoteric behavior of Bi in Hg_0.75Cd_0.25Te. The bonding characteristics between Bi and host atoms were discussed by analyzing charge densities and ELFs. The influence of Bi impurity on the electronic structure of Bi-doped Hg_0.75Cd_0.25Te was also analyzed by the calculated DOSs, band structures, and the band decomposed charge density of the defect band. It has been demonstrated that Bi can show a typical amphoteric substitution effect of group V elements.     

Full potential linearized augmented plane wave calculations of positronic and electronic charge densities of zinc-blende AlN, InN and their alloy Al0.5In0.5N

A theoretical study of electron and positron band structures of zinc-blende AlN and InN and their alloy Al_0.5In_0.5N is presented using the first-principles full-potential linearized augmented plane-wave method. Equilibrium lattices constants are determined from the total-energy minimization method. The results are compared with previous calculations and with experimental measurement. Electron and positron charge densities are computed as function of position in the unit cell. Detailed plots of distributions are along the 〈111〉 direction. The ionicity factors are calculated by means of three different approaches. The calculated results of the positron charge density reflect the high insight for the annihilation effect.     

Influence of Glycine Adsorption on Segregation of Ni-Cu (110) Surface

An atomic group model of the disordered binary alloy NixCu1-x (x=0.4) was constructed to investigate surface segregation. According to the model, the electronic structure of the NixCu1-x alloy surface was calculated by the Recursion method when glycine atoms are adsorbed on the NixCu1-x (110) surface under the condition of 0.33 coverage. The calculation results indicate that Cu is segregated on the surface of the NixCu1-x alloy, and the chemisorption of glycine restrains the segregation. In addition, the chemical adsorption of glycine greatly changes the density of states of the alloy surface near the Fermi level, and there is electric charge transfer between the alloy surface and the glycine.     

Electronic structure of TCNQ,studied with HAM/3

The electronic structure of tetracyanoquinodimethane (TCNQ) is calculated using the new semiempirical method HAM /3. The calculated photoelectron spectrum is in reasonable agreement with the measured spectrum. The excitation energies are obtained directly in HAM as the differences of the energies of the unoccupied and the occupied orbitals. The calculated UV spectrum is in good agreement with the measurements. The weak band at 5.3 eV, which earlier had been assumed to correspond to a forbidden transition, is allowed according to HAM . The electron affinity is also in reasonable agreement with the measured value. An explanation has been given for the experimental observation of several resonance states (negative electron affinities). p-Quinodimethane has also been studied.     

Molecular electronic structure of metal phthalocyanines

The molecular–electronic structure of the metal phthalocyanines (Fe, Co, Ni and Cu) has been determined by the molecular orbital treatment. Coulomb integrals of the metal atom occurring in the secular determinants have been approximated equivalent to the valence state ionization energy (VSIE) of a metal orbital for a particular charge configuration. The calculated π-electron charge densities have been found to be higher on the nitrogen atoms as compared to the other atoms in the molecule. This is in agreement with the e.s.r. studies of the metal phthalocyanines. To test the correctness of the molecular orbital calculations, the π-π* transitions (14,000 cm^?1 ? 30000 cm^?1), d-d* transitions (20000 cm^?1 ? 60000 cm^?1) and charge transfer transitions (15000 cm ^?1 ? 30000 cm^?1) have been calculated in the metal phthalocyanine molecules. The calculated frequencies have been compared with the observed ones and found in fair agreement.