scholarly journals THE PHONON SPECTRUM OF THE OCTAGONAL TILING

1993 ◽  
Vol 07 (06n07) ◽  
pp. 1505-1525 ◽  
Author(s):  
J. LOS ◽  
T. JANSSEN ◽  
F. GÄHLER
Keyword(s):  
Specific Heat ◽  
Density Of States ◽  
Phonon Spectrum ◽  
Low Frequency ◽  
Debye Model ◽  
Square Lattice ◽  
Total Density ◽  
Unit Cells ◽  
Linear Behaviour ◽  
Total Density Of States

A study of the phonon spectrum of the octagonal tiling is presented, by calculating and analysing the properties of the spectrum of perfect and randomized commensurate approximants with unit cells containing up to 8119 vertices. The total density of states, obtained by numerical integration over the Brillouin zone, exhibits much structure, and in the low frequency range of the spectrum there is deviation from the normal linear behaviour in the form of pseudogaps. For randomized approximants these pseudogaps disappear and the density of states is globally smoothened. It turns out that the widths of the gaps in the dispersion vanish in the low frequency limit. Therefore the scaling behaviour of the lowest branches tends to the behaviour of an absolutely continuous spectrum, which is not the case at higher frequencies. As an application, the vibrational specific heat of the different tiling models is calculated and compared to the specific heat of a square lattice and of a Debye model.

scholarly journals Pressure effect of the mechanical, electronics and thermodynamic properties of Mg–B compounds A first-principles investigations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
GuoWei Zhang ◽  
Chao Xu ◽  
MingJie Wang ◽  
Ying Dong ◽  
FengEr Sun ◽  
...  
Keyword(s):  
Thermodynamic Properties ◽  
First Principles ◽  
Boron Content ◽  
Structural Parameters ◽  
Debye Model ◽  
Total Density ◽  
First Principle ◽  
Volume Deformation ◽  
Temperature And Pressure ◽  
Total Density Of States

AbstractFirst principle calculations were performed to investigate the structural, mechanical, electronic properties, and thermodynamic properties of three binary Mg–B compounds under pressure, by using the first principle method. The results implied that the structural parameters and the mechanical properties of the Mg–B compounds without pressure are well matched with the obtainable theoretically simulated values and experimental data. The obtained pressure–volume and energy–volume revealed that the three Mg–B compounds were mechanically stable, and the volume variation decreases with an increase in the boron content. The shear and volume deformation resistance indicated that the elastic constant Cij and bulk modulus B increased when the pressure increased up to 40 GPa, and that MgB7 had the strongest capacity to resist shear and volume deformation at zero pressure, which indicated the highest hardness. Meanwhile, MgB4 exhibited a ductility transformation behaviour at 30 GPa, and MgB2 and MgB7 displayed a brittle nature under all the considered pressure conditions. The anisotropy of the three Mg–B compounds under pressure were arranged as follows: MgB4 > MgB2 > MgB7. Moreover, the total density of states varied slightly and decreased with an increase in the pressure. The Debye temperature ΘD of the Mg–B compounds gradually increased with an increase in the pressure and the boron content. The temperature and pressure dependence of the heat capacity and the thermal expansion coefficient α were both obtained on the basis of Debye model under increased pressure from 0 to 40 GPa and increased temperatures. This paper brings a convenient understanding of the magnesium–boron alloys.

scholarly journals Experimental and computational study on roles of WOx promoting strong metal support promoter interaction in Pt catalysts during glycerol hydrogenolysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tinnakorn Saelee ◽  
Poonnapa Limsoonthakul ◽  
Phakaorn Aphichoksiri ◽  
Meena Rittiruam ◽  
Mongkol Lerdpongsiripaisarn ◽  
...  
Keyword(s):  
Density Of States ◽  
Design Guidelines ◽  
Total Density ◽  
High Electron ◽  
Metal Support Interaction ◽  
Metal Support ◽  
Glycerol Hydrogenolysis ◽  
The Stability ◽  
Total Density Of States ◽  
Promoter Interaction

AbstractBiodiesel is of high interest due to increased demand for energy with the concern regarding more sustainable production processes. However, an inevitable by-product is glycerol. Hence, the conversion of this by-product to higher-value chemicals, especially 1,3-propanediol (1,3-PDO) via glycerol hydrogenolysis reaction, is one of the most effective pathways towards a profitable process. In general, this process is catalyzed by a highly active Pt-based catalyst supported on γ-Al2O3. However, its low 1,3-PDO selectivity and stability due to surface deactivation of such catalysts remained. This led to the surface modification by WOx to improve both the selectivity by means of the increased Brønsted acidity and the stability in terms of Pt leaching-resistance. Hence, we applied experimental and density functional theory (DFT)-based techniques to study the fundamentals of how WOx modified the catalytic performance in the Pt/γ-Al2O3 catalyst and provided design guidelines. The effects of WOx promoter on improved activity were due to the shifting of the total density of states towards the antibonding region evident by the total density of states (TDOS) profile. On the improved 1,3-PDO selectivity, the main reason was the increasing number of Brønsted acid sites due to the added WOx promoter. Interestingly, the stability improvement was due to the strong metal-support interaction (SMSI) that occurred in the catalyst, like typical high leaching-resistant catalysts. Also, the observed strong metal-support-promoter interaction (SMSPI) is an additional effect preventing leaching. The SMSPI stemmed from additional bonding between the WOx species and the Pt active site, which significantly strengthened Pt adsorption to support and a high electron transfer from both Pt and Al2O3 to WOx promoter. This suggested that the promising promoter for our reaction performed in the liquid phase would improve the stability if SMSI occurred, where the special case of the WOx promoter would even highly improve the stability through SMSPI. Nevertheless, various promoters that can promote SMSPI need investigations.

First Principles Study on Adsorption for Different Concentration of H2S on Fe(100)

2014 ◽  
Vol 1015 ◽  
pp. 521-525 ◽  
Author(s):  
Qiang Zhang ◽  
Ping Jun Hu ◽  
Qiang Luo ◽  
Yi Qiu ◽  
Zeng Ling Ran
Keyword(s):  
Density Of States ◽  
First Principles ◽  
Function Theory ◽  
Surface Adsorption ◽  
Density Function Theory ◽  
Partial Density ◽  
Total Density ◽  
Generalized Gradient ◽  
Generalized Gradient Approximation ◽  
Total Density Of States

Using the first principles method, which is based on the density function theory (DFT), the structures and electronic properties for different concentration of H2S are adsorbed on the Fe (100) surface, and their molecular orbital and absorption energies were calculated with the generalized gradient approximation. The results show that, whether one or two molecules of H2S adsorpted Fe (100) surface, adsorption of single molecules Fe (100) surface partial density of states between pure Fe (100) and two molecules, and the total density of states is mainly composed of 3d electronic contribution.

Transport properties of impurity-doped VO2

1976 ◽  
Vol 54 (4) ◽  
pp. 413-423 ◽  
Author(s):  
J. M. Reyes ◽  
M. Sayer ◽  
A. Mansingh ◽  
R. Chen
Keyword(s):  
Density Of States ◽  
Ac Conductivity ◽  
Energy Gap ◽  
Dc Conductivity ◽  
Total Conductivity ◽  
Total Density ◽  
Impurity Doped ◽  
Impurity Sites ◽  
Total Density Of States ◽  
Band Conduction

The temperature dependence of the DC conductivity in the semiconducting phase of undoped and Al, Cr, and Ti-doped VO2 has been interpreted with the aid of AC conductivity and thermopower measurements down to 77 K. A hopping conductivity is shown to be dominant for T < 180 K and to make up about 10% of the total conductivity at the metal–semiconductor transition temperature. The frequency dependence of the AC conductivity, σ~fs, is shown to be sensitive to crystalline disorder through the parameter s; s ~0.5 for 'good' crystals and 0.7–0.9 for highly doped or nonstoichiometric material. For the best crystals, a phonon drag contribution is found to exist in the thermopower. The hopping component of the DC conductivity is analyzed in terms of variable range hopping within a nonuniform density of states. For a total density of states between 1018–1020 this leads to a localization radius of 3–11 Å and the conclusion that the position of the Fermi level within the gap strongly influences the relative contributions of hopping and band conduction. A model for the density of states within the energy gap for both pure and doped VO2 is presented on the basis of localized correlations between electrons on pairs of vanadium or vanadium–impurity sites.

Investigation of the electronic structure of the SbSeBr cluster

Open Physics ◽  
2008 ◽  
Vol 6 (3) ◽  
Author(s):  
Algirdas Audzijonis ◽  
Gediminas Gaigalas ◽  
Leonardas Žigas ◽  
Audrius Pauliukas ◽  
Bronislovas Šalkus ◽  
...  
Keyword(s):  
Density Of States ◽  
Density Functional ◽  
Molecular Model ◽  
Energy Levels ◽  
Emission Spectra ◽  
Molecular Cluster ◽  
Total Density ◽  
Photoelectron Emission ◽  
Hartree Fock ◽  
Total Density Of States

AbstractThe energy levels of valence bands (VB) in SbSeBr crystals were calculated for investigation of the photoelectron emission spectra of A5B6C7 — type crystals. The molecular model of this crystal was used for calculation of VB by the Density Functional Theory (DFT) and Unrestricted Hartree — Fock (UHF) methods. The molecular cluster consisting of 20 molecules of SbSeBr was used for calculations of averaged total density of states including atom vibrations. The spectra of averaged total density of states from VB in the SbSeBr cluster were compared with experimental photoelectron emission spectra from VB of A5B6C7 — type crystals. The results of comparison clarify that the atomic vibrations are one of possible reasons for the smoother appearance of the experimental X-ray photoelectron spectrum (XPS).

Elastic Properties and Electronic Structure of WS2 under Pressure from First-principles Calculations

2017 ◽  
Vol 72 (4) ◽  
pp. 295-301 ◽  
Author(s):  
Li Li ◽  
Zhao-Yi Zeng ◽  
Ting Liang ◽  
Mei Tang ◽  
Yan Cheng
Keyword(s):  
Density Of States ◽  
First Principles ◽  
External Pressure ◽  
Band Gaps ◽  
Partial Density ◽  
Total Density ◽  
Transition Metal Dichalcogenide ◽  
First Principles Calculations ◽  
First Time ◽  
Total Density Of States

AbstractThe influence of pressure on the elastic and mechanical properties of the hexagonal transition-metal dichalcogenide WS2 is investigated using the first-principles calculations. With the increase in pressure, the lattice parameters and the volume of WS2 decrease, which is exactly in agreement with the available experimental data and other calculated results. The elastic constants Cij, bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio σ of WS2 also increase with pressure. At last, for the first time, the band gaps of energy, the partial density of states, and the total density of states under three different pressures are obtained and analysed. It is found that the band gap of WS2 decreases from 0.843 to 0 eV when the external pressure varies from 0 to 20 GPa, which implies that WS2 may transform from semiconductors to semimetal phase at a pressure about 20 GPa.

scholarly journals Probing the total density of states in a photonic crystal with different number density distributions of luminescent molecules

2004 ◽  
Vol 53 (1) ◽  
pp. 132
Author(s):  
Liu Xiao-Dong ◽  
Li Shu-Guang ◽  
Xu Xing-Sheng ◽  
Wang Yi-Quan ◽  
Cheng Bing-Ying ◽  
...  
Keyword(s):  
Photonic Crystal ◽  
Density Of States ◽  
Total Density ◽  
Number Density ◽  
Density Distributions ◽  
Total Density Of States

scholarly journals Tight-binding dispersion of the prismatic pentagonal lattice

2018 ◽  
Vol 32 (01) ◽  
pp. 1750273
Author(s):  
Susobhan Paul ◽  
Asim Kumar Ghosh
Keyword(s):  
Band Structure ◽  
Density Of States ◽  
Parameter Space ◽  
Tight Binding ◽  
Dispersion Relations ◽  
Total Density ◽  
Zero Energy ◽  
Dirac Cone ◽  
Analytic Expressions ◽  
Total Density Of States

Tight-binding Hamiltonian on the prismatic pentagonal lattice is exactly solved to obtain the analytic expressions of dispersion relations and eigenvectors. This lattice is made of prismatic pentagon which is different from Cairo pentagon. Six different dispersion relations and total density of states are obtained. Dispersion relations are symmetric about the zero energy at a particular point in the parameter space. Although a large gap is found for the Cairo pentagonal lattice, no gap as well as no Dirac cone is found to appear in the tight-binding band structure for this prismatic pentagonal lattice. Instead, a pair of van Hove singularities has been identified at two different energy values in the band structure.

scholarly journals Electronic Transitions, Inter- and Intra-Bond Interactions of an Azabicycle Single Crystal using DFT

2021 ◽  
Vol 33 (10) ◽  
pp. 2365-2372
Author(s):  
J. Dineshkumar ◽  
S. Subashchandrabose ◽  
S. Niaz ◽  
P. Parthiban
Keyword(s):  
Functional Groups ◽  
Density Of States ◽  
Electronic Transitions ◽  
Partial Density ◽  
Electronic Charge ◽  
Total Density ◽  
X Ray Diffraction ◽  
Mannich Condensation ◽  
Td Dft ◽  
Total Density Of States

2,4-Diphenyl-3-azabicyclo[3.3.1]nonan-9-one O-benzyloxime (ABN-OBn) was synthesized by modified Mannich condensation, purified by recrystallization and single crystals were grown by slow evaporation from ethanol. The empirical formula of the molecule is C27H28N2O as witnessed by HRMS, elemental analysis and the X-ray diffraction. The crystal belongs to triclinic system (α = 73.640, β = 78.505, γ = 87.078) with P-1 space group. The electronic excited states of ABN-OBn have been calculated using TD-DFT/B3LYP/6-31G(d,p) level of theory, in order to investigate the electronic transitions within the molecule. Frontier molecular orbitals (FMOs) of ABN-OBn have been studied to understand the electronic charge distributions and its band gap (5.0514 eV/245.45 nm). Density of states (DOS), partial density of states (PDOS) and total density of states (TDOS) with respect to functional groups were computed to investigate the electron densities of functional groups in the molecule. Natural bond orbital (NBO) has been performed to explore the intramolecular π-π* interaction of the compound.

First-Principles Study on Ga-N Co-Doped P-Type ZnO

2011 ◽  
Vol 299-300 ◽  
pp. 498-502 ◽  
Author(s):  
Hong Sheng Zhao ◽  
Yu Dan Gu ◽  
Nan Zhang ◽  
Ya Hong Gao
Keyword(s):  
Density Of States ◽  
Density Functional ◽  
Partial Density ◽  
Total Density ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Donor Acceptor ◽  
P Type ◽  
Total Density Of States ◽  
Co Doped

Based on the density functional theory, the structure of pure ZnO, N doped, and Ga-N/Ga-2N co-doped wurtzite ZnO was calculated by using first-principle plane wave ultrasoft pseudopotential method. Electronic structures of these ZnO-based doping syetems were studied. The calculations of band structure, total density of states, and partial density of states show that Ga-2N donor/acceptor co-doped ZnO is easier to implement the p-type ZnO than other cases.

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