Dynamic structure factor and vibrational properties of SiO2 glass.

The search for conventional superconductors with high transition temperatures ( $${T}_{c}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) has largely focused on intrinsically metallic compounds. In this work, we explore the potential of intrinsically non-metallic compounds to exhibit high- $${T}_{c}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> </mml:math> superconductivity under ambient pressure through carrier doping. We identify MgAlFeH 6 , a representative of carrier-doped transition-metal hydrides like Mg 2 FeH 6 , as a promising example with a predicted $${T}_{c}\approx 130\,{\rm{K}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>130</mml:mn> <mml:mspace/> <mml:mi>K</mml:mi> </mml:mrow> </mml:math> . We propose that the average projected electron density of states (DOS), defined as the geometric mean of the total and hydrogen-projected DOS at the Fermi level, serves as a simple and computationally inexpensive indicator of high- $${T}_{c}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> </mml:math> behavior. Notably, the correlation between $${T}_{c}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> </mml:math> and the average projected DOS is stronger than that between $${T}_{c}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> </mml:math> and either total DOS or hydrogen-projected DOS. We also highlight the tradeoff between high- $${T}_{c}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> </mml:math> and dynamic stability, both of which depend on the electron DOS at the Fermi level. Our findings thus expand the pool of potential superconducting materials and offer a practical route for accelerating the discovery of superconductors suitable for real-world applications.

Using an analytic method involving continued fractions, we calculate the site-site, two-time Green's functions for a general one-dimensional crystal. These Green's functions give the electron correlations for a tight-binding model in the noninteracting-electron approximation, or the displacement correlations of a vibrating system with harmonic interatomic forces. The Green's functions can be summed in closed form to give the density of states for either model. The resulting expression depends only on the trace of a ``transfer matrix,'' and on its derivative with respect to energy. We use this formula to determine the densities of states of a large class of quasiperiodic models, and we check our results against perturbation-theory calculations of the band structure of our models. From the Green's functions, we also derive an expression for the dynamic structure factor of our vibrating-lattice model, and we derive a class of iteration relations which allow us to evaluate it very rapidly for quasiperiodic chains. We give results for two different quasicrystals, and compare them against known general restrictions on the form of the dynamic structure factor.

A slab approach in the framework of ab initio calculations was applied to study surface electronic states in In 2 O 3 crystal. Density functional theory (DFT) calculations were carried out employing the WIEN 2k code and using the full potential method with Augmented Plane Waves + local orbitals (APW+lo) formalism. Total and partial DOS (Density of States) were calculated for In and O atoms in two upper (110) surface layers. Comparison of total and partial DOS allowed determining a contribution of electronic states of different In and O surface atoms into formation of surface electronic spectra and corresponding chemical bonds. A dominant ionic character of chemical bonds in In 2 O 3 is found. Calculations were performed for three slab models with different geometry parameters. It was shown that an optimal ratio between the whole vertical size of a supercell and the vertical size of atomic cluster has to be chosen. The size of vacuum region in the slab model influences significantly on the reliability of calculated characteristics of the surface electronic structure. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

The new compounds, Mg(BiO2)4 was synthesized and structurally characterized semiconductor. Due to theoretical investigation for both of Mg(BiO2)4 and Mg(Bi0.91Ge0.083O2)4, computational tools were used. To calculated the electronic band structures, the total density of state, the partial density of state, and optical properties were used Generalized Gradient Approximation (GGA) based on the Perdew–Burke–Ernzerhoff (PBE0) using first principle method for Mg(BiO2)4. The band gap was recorded 0.545 eV which is supported for good semiconductor. The density of states was simulated for evaluating the nature of 3s, 3p for Mg, 6s 6p, 4d, and 2s, 2p for O atoms. Furthermore, the optical properties including absorption, reflection, refractive index, conductivity, dielectric function, and loss function were simulated which can account for the superior absorption of the visible light. The key point of this research to determine the activity of Ge doped by 11.0%, whereas the band gap, density of state, and optical properties were affected. Analysis of the band gap and optical properties of both of Mg (BiO2)4 and Mg(Bi0.91Ge0.083O2)4, the Ge doped shows the high conductivity than undoped.

We study the spectral width as a function of the external momentum for the dynamical structure factor of a disordered harmonic solid, considered as a toy model for supercooled liquids and glasses. In the contexts of both the single-link coherent potential approximation and a single-defect approximation, two different regimes are clearly identified: if the density of states at zero energy is zero, the usual p(4) law is recovered for small momentum. On the contrary, if the disorder induces a nonvanishing density of states at zero energy, a linear behavior is obtained. The dynamical structure factor is numerically calculated in lattices as large as 96(3) and satisfactorily agrees with the analytical computations.

Dynamic structure factor of crosslinked polymer blends

The electronic properties of 4,4′-bis(3-ethyl-N-carbazolyl)-1,1′-biphenyl (ECBP) have been studied using time-dependent density functional theory. The non-linear optical (NLO) properties and dipole moments were investigated to understand the optical behavior of ECBP. Frontier molecular orbitals were determined to define the energetic properties of the title molecule. The total density of states, partial density of states, and overlap population electronic density of states of ECBP were calculated and analyzed. Experimental and semi-theoretical parameters such as the optical density, transmittance, absorbance band edge, optical bandgap, refractive index, incidence angle, and refraction angle of ECBP at 3 mM, 10 mM, 21 mM, and 70 mM were obtained. The results indicate that this molecule is a suitable material for NLO, optical, and optoelectronic devices.

The ionic dynamic structure factor is examined to assess the relative roles of dissipation and the effective ionic interaction. Two disparate physically based models of dissipation, which can differ numerically by orders of magnitude, are used in molecular dynamics. We find a negligible impact on the amplitudes of the dynamic structure factors for physically realistic parameter values. We then examine the effective ionic interaction by varying its strength, the size of the atomic core (through a pseudopotential), and the screening model. We find that "diffusive" peaks in the dynamic structure factor are very sensitive to the form of the ionic interaction, and this sensitivity arises primarily from atomic physics through the pseudopotential. This suggests that it would be useful to employ the measured zero-frequency dynamic structure factor S_{ii}(k,0) as a constraint on the effective interaction, which in turn can be used to compute physical properties.

Synthesis and transport properties of La2NiO4

This paper studies the effect of GGA-PBE, GGA-PBEsol, GGA-PW91, GGA-VWN-BP, LDA-PWC, LDA-VWN parameterized exchange–correlation functionals and Cu impurity concentration on the lattice and electronic properties of bulk AuCu by the Density Functional Theory (DFT). The lattice properties are determined by the lattice constant, the unit cell volume and the total energy on unit cell. The electronic properties are determined by the band gap, the Partial Density of States (PDOS) and the total Density of States (DOS) of materials. The obtained results showed the effect of the interaction potential and the Cu impurity concentration on the lattice structure and the electronic structure of bulk AuCu.

How to develop a new, efficient photo catalyst is still a big challenge to us. A suitable band gap is the key for light absorption of semiconductor. Herein, an innovative anion intercalation strategy is, for the first time, developed to regulate the energy band of semiconductor. Typically, we introduce a layered sulfate compound (Bi2O(OH)2SO4) as a new photo catalyst, which has not been known before. Both partial density of states (PDOS) and total density of states (TDOS) have demonstrated that compared with Bi2O3 (2.85 eV), the band gap of Bi2O(OH)2SO4 has been widened to 4.18 eV by the intercalation of sulfate anion. Moreover, the band gap width of oxyacid salt compound is mainly predominated by the number of the outmost electrons (NOE) of central atom of anion. This study suggests that new photo catalysts can be developed by grouping anions with the existing oxides or sulfides.

First principles investigations of optoelectronic and magnetic properties of co-doped zinc sulphide by 3d and 4f elements

First-principles calculations to investigate band gap of cubic BaThO3 with systematic isotropic external static pressure and its impact on structural, elastic, mechanical, anisotropic, electronic and optical properties

The structural, elastic, electronic, and thermodynamic properties of thermoelectric material MgAgSb in γ,β,α phases are studied with first-principles calculations based on density functional theory. The optimized lattice constants accord well with the experimental data. According to the calculated total energy of the three phases, the phase transition order is determined from α to γ phase with cooling, which is in agreement with the experimental result. The physical properties such as elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and anisotropy factor are also discussed and analyzed, which indicates that the three structures are mechanically stable and each has a ductile feature. The Debye temperature is deduced from the elastic properties. The total density of states (TDOS) and partial density of states (PDOS) of the three phases are investigated. The TDOS results show that the γ phase is most stable with a pseudogap near the Fermi level, and the PDOS analysis indicates that the conduction band of the three phases is composed mostly of Mg-3s, Ag-4d, and Sb-5p. In addition, the changes of the free energy, entropy, specific heat, thermal expansion of γ-MgAgSb with temperature are obtained successfully. The obtained results above are important parameters for further experimental and theoretical tuning of doped MgAgSb as a thermoelectric material at high temperature.

Effects of chlorine adatoms on small lithium nanoclusters adsorbed on graphene