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The structural, elastic and electronic properties of four nitrides M 2 N 3 (M = Zr, Hf, W and Re) with U 2 S 3 structure are investigated by plane-wave pseudopotential density functional theory by the generalized gradient approximation in this paper. The calculated elastic constants show that the nitrides are mechanically stable at ambient conditions, except Re 2 N 3 . The calculated bulk modulus B and shear modulus G indicate that Zr 2 N 3 , Hf 2 N 3 and W 2 N 3 are potential candidates for hard materials. [ABSTRACT FROM AUTHOR]

The structural, electronic, and optical properties of cubic perovskite NaMgF3 are calculated by plane-wave pseudopotential density functional theory. The calculated lattice constant a0, bulk modulus B0, and the derivative of bulk modulus B′0 are 3.872 Å, 78.2 GPa, and 3.97, respectively. The results are in good agreement with the available experimental and theoretical values. The electronic structure shows that cubic NaMgF3 is an indirect insulator with a wide forbidden band gap of Eg = 5.90 eV. The contribution of the different bands is analyzed by total and partial density of states curves. Population analysis of NaMgF3 indicates that there is strong ionic bonding in the MgF2 unit, and a mixture of ionic and weak covalent bonding in the NaF unit. Calculations of dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, optical reflectivity, and conductivity are also performed in the energy range 0 to 70 eV. [ABSTRACT FROM AUTHOR]

In the present paper we give a detailed report on the results of our first-principles investigations of Ar adsorptions at the four high symmetry sites on M (111) (M = Pd, Pt, Cu, and Rh) surfaces. Our studies indicate that the most stable adsorption sites of Ar on Pd (111) and Pt (111) surfaces are found to be the fcc-hollow sites. However, for Ar adsorptions on Cu (111) and Rh (111) surfaces, the most favorable site is the on-top site. The density of states (DOS) is analyzed for Ar adsorption on M (111) surfaces, and it is concluded that the adsorption behavior is dominated by the interaction between 3s, 3p orbits of Ar atoms and the d orbit of the base metal atoms. [ABSTRACT FROM AUTHOR]

The adsorption behavior of H2 on the LiB (001) surface was investigated with density functional theory (DFT) method. It was found that the site of H2 adsorbed on the Li-B bridge II was easier than the other four sites (Li top, B top, hollow vertical and Li-B bridge I). H2 adsorbed on the Li-B bridge II site was a strong chemical adsorption. The adsorption energy was 2.190 eV, and the H, B atoms exhibited covalent characteristics, the H--H atoms have a little interaction, and the H2 was 0.331 Å below the surface of Li-B bridge II. The charge density, band structure, totals and partial density of states were calculated utilizing the first principle method. These calculations showed that the H interacted with the surface atoms, and partially saturated the dangling bonds with the surface atoms. The interaction between H and the surface atoms were mainly attributed to the H 1s, B 2s and B 2p states. The calculated band gap was 0.075 eV and 0.199 eV before and after adsorption. [ABSTRACT FROM AUTHOR]

Orbital responses to methyl sites in CnH2n+2 (n = 1-6) are studied by B3LYP/TZVP based on the most stable geometries using the B3LYP/aug-cc-pVTZ method. Vertical ionization energies are produced using the SAOP/et-pVQZ model for the complete valence space. The highest occupied molecular orbital (HOMO) investigations indicate the pelectron profiles in methane, ethane, propane, and n-butane. By increasing the number of carbon-carbon bonds in lower momentum regions, the s, p-hybridized orbitals are built and display strong exchange and correlation interactions in lower momentum space (P . 0.50 a.u.). Meanwhile, the relative intensities of the isomers in lower momentum space show the strong bonding number dependence of the carbon-carbon bonds, meaning that more electrons have contributed to orbital construction. The study of representative valence orbital momentum distribution further confirms that the structural changes lead to evident electronic rearrangement over the whole valence space. An analysis based on the isomers reveals that the valence orbitals are isomer-dependent and the valence ionization energy experiences an apparent shift in the inner valence space. However, such shifts are greatly reduced in the outer valence space. Meanwhile, the opposite energy shift trend is found in the intermediate valence space. [ABSTRACT FROM AUTHOR]

We use heat-capacity measurements as a function of field rotation to identify the nodal gap structure of CeIrIn5 at pressures to 2.05 GPa, deep inside its superconducting dome. A fourfold oscillation in the heat capacity at 0.3 K is observed for all pressures, but with its sign reversed between 1.50 and 0.90 GPa. On the basis of recent theoretical models for the field-angle-dependent specific heat, all data, including the sign reversal, imply a Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. order parameter with nodes along [110], which constrains theoretical models of the pairing mechanism in CeIrIn5. [ABSTRACT FROM AUTHOR]

A theoretical study of structural and electronic properties of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX) crystal is performed using density functional theory. The band structure, the total density of states, the atomic orbit projected density of states (PDOS) of C, N, O, and H, and Mulliken population analysis are discussed. The study by analyzing the PDOS shows that the structure of BCHMX crystal possesses CH···O intra- and intermolecular hydrogen bonding. There are hydrogen bonds between H3-1s and O5-2p orbits, H2-1s and O6-2p orbits of intramolecules and between H2-1s and O1-2p orbits of intermolecules. The reasons for the smaller impact sensitivity compared with β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane and 1,3,5-trinitro-1,3,5-triazinane are also explored from the band gap in the crystal and the weakest bond dissociation energy in single molecule. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: BC5 is a newly synthesized superhard material. We present a systematic investigation of optical properties of BC5 in P3m1 and I-4m2 phases at ambient and high pressure in the framework of density functional theory with the generalized gradient approximation (GGA) in this paper. Optical properties such as dielectric function, refractive index, absorption, reflectivity and electron energy-loss spectrum are obtained successfully. The feature in the spectra of the optical parameters is discussed. Through calculation, we find BC5 is optically anisotropic. Moreover, the dielectric function exhibits a large change at 70GPa pressure for P3m1 BC5 phase, but I-4m2 phase not, indicating the stable electronic structure that the I-4m2 phase possesses. [Copyright &y& Elsevier]

Abstract: We present a systematic theoretical study for the structural, elastic and electronic properties of TaB2 with AlB2 structure under pressures ranging from 0GPa to 120GPa within the framework of density-functional theory in this paper. The results at zero pressure are in good agreement with available theoretical and experimental values. Our attention has been focused on high pressure behavior of TaB2. The pressure dependence of structure, elastic constants, Debye temperature, and density of states (DOS) are successfully calculated and discussed. [ABSTRACT FROM AUTHOR]

Abstract: A systematic theoretical study is presented for the structural and electronic properties of HfB2 with AlB2 structure under pressure ranging from 0 to 240GPa in the framework of density functional theory. The results at zero pressure are in good agreement with the available theoretical and experimental values. The pressure dependence of structural property shows that the effect of pressure is little on the structure of HfB2. The density of states (DOS) of HfB2 versus pressure is also successfully calculated. We find high pressure greatly changes the profile of the DOS, but it hardly changes the DOS value at Fermi level. Meanwhile, the Mulliken population analyses are investigated. It is suggested that as the pressure increases, a number of charge transfer from Hf to B atoms. [Copyright &y& Elsevier]

The properties of 2-Nitrimino-1-nitroimidazolidine are calculated by using SIESTA code, which adopts the standard Kohn-Sham self-consistent density functional method in the local density approximation. The structures and electronic properties are analyzed, and the factors that affect the impact sensitivity are discussed based on the crystal structure, band energy, and projected density of state. The reason for the smaller impact sensitivity compared to RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) is also explored from several respects such as the weakest bond dissociation energy in single molecule, and hydrogen bond, band gap in the crystal. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

Abstract  We present density functionary theory (DFT) calculations on the structural parameters and electronic structure for iridium nitride by using the generalized gradient approximation (GGA) and the Perdew–Burke–Ernserhof (PBE) exchange-correlation functional. The lattice parameters and bulk modulus (B 0) for the ground state are obtained, and the energy band structure and electron densities of states (DOS) of IrN2 are presented. It is found that IrN2 has a very close indirect energy gap. There is a strong covalent bond between the two nearest N atoms. This gives rise to a very high elastic modulus of IrN2 and reveals the quasimolecular nature of the N2 in IrN2 crystal. Lattice parameters, bulk modulus, and the electronic structure of IrN2 under high pressure have also been investigated based on DFT. The compressibility along three cell vectors is very close to each other. The band gap increases a little with the pressure even when the pressure is up to 100 Gpa. [ABSTRACT FROM AUTHOR]

Endohedral metallofullerenes (EMFs) have been extensively studied since their discovery in 1985. Metal-metal bonds, nevertheless, have never been explicitly observed in EMFs synthesized so far. In this contribution, we show by means of all-electron relativistic density functional computations that the dimetalloendofullerene, U2@C60, has an unprecedented U-U multiple bond consisting solely of sixfold ferromagnetically coupled one-electron-two-center bonds with the electronic configuration (5fπu)²(5fσg)1- (5fδg)²(5fΦu)¹, which are dominated by the uranium 5f atomic orbitals. This bonding scheme is completely distinct from the metal-metal bonds discovered thus far in the d- and f-block polynuclear metal complexes. This finding initiates a connection of the metal-metal multiple bonding chemistry and the fullerene chemistry. [ABSTRACT FROM AUTHOR]

Metal carbide compound containing highly charged C2q-(q 5, 6) moiety is rather scarce. We show by means of density functional calculations that an unprecedented 4-C26-anion can viably exist as an endohedral Sc4C26cluster in the endofullerene Sc4C2C80. The electronic structure, ionization energy, electron affinity, 13C NMR chemical shifts, vibrational frequencies, and electrochemical redox potentials of this unique endofullerene have been predicted to assist future experimental characterization. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have shown that the open-shell metal−carbide endofullerene Sc3C2@C80 has the valence state (Sc3+)3(C2)3-@C806-. A lot of low-lying isomers differing in geometries and locations of the endohedral [(Sc3+)3(C2)3-] cluster have been located, indicating unusual dual intramolecular dynamic behaviors of this endofullerene at room temperature. The electrochemical redox properties of this endofullerene have been elucidated in terms of electronic structure theory. Its redox states are found to follow the general charge−state formula (Sc3+)3C2(3-q)-@C806- (q is the charge of the whole molecule ranging from +1 to −3), demonstrating the high charge flexibility of the endohedral metal−carbide cluster. The structure of the endohedral [(Sc3+)3C2(3-q)-] cluster varies with the redox processes, shifting from a planar structure (for q = 0 and −1) to a trifoliate structure (for q = +1, −2, −3). [ABSTRACT FROM AUTHOR]

Using first-principles methods, we investigated the effect of structural deformation on the electronic and magnetic properties of Sr 3 Ir 2 O 7 by two tuning ways: reducing only the interlayer spacing and the uniaxial-like compression. In both cases, an insulator-metal transition is successfully achieved with significantly different Fermi surface features. The former consists of a hole pocket and an electronic pocket, while for the latter, a pseudo-gap is captured near the center of the crystallographic Brillouin zone. The anti-ferromagnetism collapses completely and is not fully synchronized with the closing of the Mott gap in two kinds of compression cases, indicating that the conventional correlation between magnetic order and Mott insulating state does not exist here. Our research is conducive to understand the nature of lattice distortion-induced electronic and magnetic transitions, and will be expected to provide a new theoretical reference for the experimental regulation of novel metallic properties in iridium. [ABSTRACT FROM AUTHOR]

Our calculations demonstrate that the concentration of neutral oxygen vacancies can affect the geometrical structrue, electronic structure, and optical properties of α-quartz. Moreover, the distribution of the neutral oxygen divacancy can also exert some influence on the properties of α-quartz. The dissimilarity and similarities are presented in the corresponding density of state (DOS) and absorption spectrum. In addition, when a higher defect concentration is involved in α-quartz, the influence of center on the geometry of α-quartz becomes more significant. However, the introduction of an center barely results in any improvement compared with the influence produced by the corresponding neutral defect. [ABSTRACT FROM AUTHOR]

The structural, electronic, and optical properties of rutile—, CaCl2−, and PdF2—ZnF2 are calculated by the plane-wave pseudopotential method within the density functional theory. The calculated equilibrium lattice constants are in reasonable agreement with the available experimental and other calculated results. The band structures show that the rutile—, CaCl2−, and PdF2—ZnF2 are all direct band insulator. The band gaps are 3.63, 3.62, and 3.36 eV, respectively. The contribution of the different bands was analyzed by the density of states. The Mulliken population analysis is performed. A mixture of covalent and weak ionic chemical bonding exists in ZnF2. Furthermore, in order to understand the optical properties of ZnF2, the dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, and optical reflectivity are also performed in the energy range from 0 to 30 eV. It is found that the main absorption parts locate in the UV region for ZnF2. This is the first quantitative theoretical prediction of the electronic and optical properties of ZnF2 compound, and it still awaits experimental confirmation. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, we investigate the effects of two kinds of oxygen defects on the electronic and magnetic properties in SrIrO 3 bulk. One is the oxygen defect in IrO 2 plane (Ov1) and the other out-of-plane (Ov2). The results show that both oxygen defects enhance the inherent metallicity of the crystal and there is no tendency to achieve the Mott transition. Most surprised, we find that a small out-of-plane magnetic moment along c axis is formed due to the apical tilting of the defective octahedrons induced by the in-plane oxygen defects. While a local and weak ab in-plane ferromagnetic response comes from the out-of-plane defect which destroys the connectivity between adjacent layers and promotes a small in-plane rotation. In addition to the distortion of the defective blocks, the weak ferromagnetic phenomenon is also limited by the concentration of oxygen defects. Our research indicates that non-equivalent oxygen deficiencies exert distinct regulatory roles on the magnetic properties. [ABSTRACT FROM AUTHOR]

Recently, single-layer group III monochalcogenides have attracted both theoretical and experimental interest at their potential applications in photonic devices, electronic devices, and solar energy conversion. Excited by this, we theoretically design two kinds of highly stable single-layer group IV-V (IV=Si,Ge, and Sn; V=N and P) and group V-IV-III-VI (IV=Si,Ge, and Sn; V=N and P; III=Al,Ga, and In; VI=O and S) compounds with the same structures with single-layer group III monochalcogenides via first-principles simulations. By using accurate hybrid functional and quasiparticle methods, we show the single-layer group IV-V and group V-IV-III-VI are indirect bandgap semiconductors with their bandgaps and band edge positions conforming to the criteria of photocatalysts for water splitting. By applying a biaxial strain on single-layer group IV-V, single-layer group IV nitrides show a potential on mechanical sensors due to their bandgaps showing an almost linear response for strain. Furthermore, our calculations show that both single-layer group IV-V and group V-IV-III-VI have absorption from the visible light region to far-ultraviolet region, especially for single-layer SiN-AlO and SnN-InO, which have strong absorption in the visible light region, resulting in excellent potential for solar energy conversion and visible light photocatalytic water splitting. Our research provides valuable insight for finding more potential functional two-dimensional semiconductors applied in optoelectronics, solar energy conversion, and photocatalytic water splitting. [ABSTRACT FROM AUTHOR]