Unveiling the Atomic and Electronic Structure of Stacked-Cup Carbon Nanofibers

AbstractWe report results of comprehensive experimental exploration (X-ray photoemission, Raman and optical spectroscopy) of carbon nanofibers (CNFs) in combination with first-principles modeling. Core-level spectra demonstrate prevalence of sp2 hybridization of carbon atoms in CNF with a trace amount of carbon–oxygen bonds. The density functional theory (DFT)-based calculations demonstrated no visible difference between mono- and bilayers because σ-orbitals are related to in-plane covalent bonds. The influence of the distortions on π-peak is found to be significant only for bilayers as a result of π–π interlayer bonds formation. These results are supported by both experimental Raman and XPS valence band spectra. The combination of optical measurements with a theoretical modeling indicates the formation of optically active graphene quantum dots (GQDs) in the CNF matrix, with a radiative relaxation of the excited π* state. The calculated electronic structure of these GQDs is in quantitative agreement with the measured optical transitions and provides an explanation of the absence of visible contribution from these GQDs to the measured valence bands spectra.

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Theoretical study on the electronic structure, mechanical property, and thermal expansion of yttrium oxysulfide

International Journal of Computational Materials Science and Engineering ◽

10.1142/s2047684115500049 ◽

2015 ◽

Vol 04 (01) ◽

pp. 1550004

Author(s):

Ruipeng Gao ◽

Yefei Li

Keyword(s):

Mechanical Property ◽

Thermal Expansion ◽

Electronic Structure ◽

Bulk Modulus ◽

Density Functional ◽

Theoretical Study ◽

Spherical Shape ◽

Weak Anisotropy ◽

Covalent Bonds ◽

Very High

The electronic structure, mechanical property and thermal expansion of yttrium oxysulfide are calculated from first-principles using the theory of density functional. The calculated cohesive energy indicates its thermodynamic stable nature. From bond structure, the calculated bandgap is obtained as 2.7 eV; and strong covalent bonds exist between Y and O atoms intra 2D [ Y – O ] layer in material, while relatively weak covalent bonds also exist inter 2D [ Y – O ] layer and S atoms. From simulation, it is found that the bulk modulus is about 119.4 GPa for the elastic constants, and the bulk modulus shows weak anisotropy because the surface contours of them are close to a spherical shape. The calculated B/G clearly implies its ductile nature, and the Y 2 O 2 S phase can also be compressed easily. The temperature dependence of thermal expansions is mainly caused by the restoration of thermal energy due to lattice excitations at low temperature. When the temperature is very high, the thermal expansion coefficient increases linearly with temperature increasing. Meanwhile, the heat capacities are also calculated and discussed by thermal expansion and elasticity.

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Renormalization from Density Functional Theory to Strong Coupling Models for the Electronic Structure of La2CuO4

MRS Proceedings ◽

10.1557/proc-169-19 ◽

1989 ◽

Vol 169 ◽

Cited By ~ 1

Author(s):

Mark S. Hybertsen ◽

Michael Schluter ◽

E.B. Stechel ◽

D.R. Jennison

Keyword(s):

Electronic Structure ◽

Hubbard Model ◽

Strong Coupling ◽

Density Functional ◽

Nearest Neighbor ◽

Quantitative Agreement ◽

Energy Scale ◽

Low Energy ◽

Energy Spectra ◽

Functional Theory

AbstractStrong coupling models for the electronic structure of La2CuO4 are derived in two successive stages of renormalization. First, a three-band Hubbard model is derived using a constrained density functional approach. Second, exact diagonalization studies of finite clusters within the three band Hubbard model are used to select and map the low energy spectra onto effective one-band Hamiltonians. At each stage, some observables are calculated and found to be in quantitative agreement with experiment. The final results suggest the following models to be adequate descriptions of the low energy scale dynamics: (1) a spin 1/2 Heisenberg model for the insulating case with nearest neighbor J≈130 meV; (2) a "t–t'–J" model with nearly identical parameters for the electron and hole doped cases.

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First-Principles Study on Electronic Structure, Elasticity, Debye Temperature and Anisotropy of Cubic KCaF3

Materials Science Forum ◽

10.4028/www.scientific.net/msf.999.109 ◽

2020 ◽

Vol 999 ◽

pp. 109-116

Author(s):

Xing Liu ◽

Jia Fu ◽

Man Man Han ◽

Kai Xin Sun ◽

Sheng Li Wei

Keyword(s):

Electronic Structure ◽

Debye Temperature ◽

First Principles ◽

Density Functional ◽

Elastic Moduli ◽

Poisson Ratio ◽

Structural Parameters ◽

Functional Material ◽

Covalent Bonds ◽

Functional Theory

As a potential functional material in the perovskite family, the KCaF3 on electronic structure, elasticity, Debye temperature and anisotropy are studied based on density functional theory (DFT). Above all, the structural parameters of KCaF3 crystal are optimized. Then the elastic constants and Debye temperature are calculated. The results show that: (1) KCaF3 is composed of covalent bonds, in which the Ca-F bond is stronger than K-F. (2) Ca atom mainly contributes for the electronic properties of KCaF3. (3) The structural parameters of KCaF3 is in fair agreement with the experimental data. (4) The anisotropy of KCaF3 was analyzed from the pure and quasi waves, of which the longitudinal wave velocity in the direction of [100] is the larger than the others two directions ([110] and [111]). Finally, The homogenized elastic moduli (bulk modulus B, shear modulus G, Young's modulus E), Pugh and Poisson ratio, are obtained. This research is meaningful and thus to provides a good theoretical guidance for the design the new ABX3-type material with better performance.

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First-principles investigation of MoS2 monolayer adsorbed on SiO2 (0001) Surface

Modern Physics Letters B ◽

10.1142/s0217984917502293 ◽

2017 ◽

Vol 31 (25) ◽

pp. 1750229 ◽

Cited By ~ 5

Author(s):

Xiangying Su ◽

Hongling Cui ◽

Weiwei Ju ◽

Yongliang Yong ◽

Xiaohong Li

Keyword(s):

Density Functional Theory ◽

Electronic Structure ◽

Charge Transfer ◽

First Principles ◽

Density Functional ◽

Density Functional Theory Calculations ◽

Interlayer Spacing ◽

Covalent Bonds ◽

Functional Theory ◽

Mos2 Monolayer

In this paper, the geometric and electronic structure of MoS2 monolayer (ML) adsorbed on SiO2 (0001) surface were studied by using density functional theory calculations. The calculated interfacial binding energy shows that the MoS2/SiO2 hybrid system is stable. MoS2 ML is bound to the SiO2 surface with a big interlayer spacing and no covalent bonds form at the interface. The study of the density of states and the charge transfer indicates that the interaction between MoS2 ML and the SiO2 substrate is very weak. As a result, the electronic properties of MoS2 ML are almost not affected by the SiO2 substrate. This work will be beneficial to the design of MoS2 ML-based devices where a substrate is needed.

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Hydrothermal synthesis of biocompatible nitrogen doped graphene quantum dots

Energy & Environment ◽

10.1177/0958305x20984112 ◽

2021 ◽

pp. 0958305X2098411

Author(s):

Wan Ibtisam Wan Omar ◽

Chin Fhong Soon ◽

Mohd Khairul Ahmad ◽

Masaru Shimomura

Keyword(s):

Quantum Dots ◽

Electronic Structure ◽

Hydrothermal Synthesis ◽

Density Functional ◽

Theoretical Calculations ◽

Graphene Quantum Dots ◽

Biological Application ◽

Nitrogen Doped ◽

Nitrogen Doped Graphene ◽

Doped Graphene

Nitrogen-doped graphene quantum dots (N-GQDs) are promising biocompatible nanomaterial which has received much attention for biological application. However, the effect of the engineered electronic structure of N-GQDs to the fluorescence of GQDs applied for bio-imaging is still under debate. In this study, N-GQDs were synthesized by a facile one-step hydrothermal method for 10 hours at 180°C and theoretical calculation of electronic structure using density functional theory (DFT) by GAUSSIAN 09, were compared. Single to multilayer of N-GQDs with the particle size of 3.2 nm in average were obtained from hydrothermal synthesis. The optical properties of N-GQDs emitted green photoluminescence (PL) at 525 nm (2.36 eV) with PL excitation (PLE) at 367 nm (3.38 eV). From DFT calculation, the optoelectronic properties of GQDs from HOMO to LUMO differ between edge functionalization and graphitic nitrogen doping. Furthermore, cells cytotoxity showed that N-GQDs possess non-toxic property, and the cells were presented with high viability. In summary, by comparing experimental and theoretical calculations, the electronic properties of N-GQDs could enhance their reactivity in photo-electronics for biological application.

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THE ELECTRONIC STRUCTURE AND MAGNETISM OF CrSb WITH LATTICE CONSTANTS

International Journal of Modern Physics B ◽

10.1142/s0217979211058237 ◽

2011 ◽

Vol 25 (05) ◽

pp. 653-664 ◽

Cited By ~ 1

Author(s):

LI CHEN

Keyword(s):

Crystal Structure ◽

Electronic Structure ◽

Lattice Constant ◽

Magnetic Moment ◽

Density Functional ◽

Covalent Bonds ◽

Lattice Constants ◽

Atom Increase ◽

Nias Type ◽

Type Crystal

The electronic structure and magnetism of CrSb compounds have been studied by a periodic quantum-mechanical calculation based on density functional theory. The results show that a ferrimagnetic ordered phase of CrSb in the Zinc-blende structure (ZB) is stable with half metallic properties, whereas the antiferromagnetic phase of CrSb in the NiAs -type crystal structure is energetically favored with no-gap band. The lattice constants have significant influence on the magnetism of CrSb . The band gap and the magnetic moment of Cr atom increase with increasing lattice constant in ZB CrSb . The effects on magnetic moment in the NiAs -type crystal structure are more sensitive substantially to the change of lattice constant a as compared with that of the lattice constant c. It is found that apart from ionic or metallic bonds there are covalent bonds between Cr d and Sb p orbitals in ZB CrSb , while bonding between Cr and Sb atoms is mainly ionic or metallic in CrSb of NiAs structure.

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The pressure dependence of physical properties of (W2/3Ti1/3)3AlC2 and its counterpart W3AlC2 by first-principles calculations

Modern Physics Letters B ◽

10.1142/s0217984917503262 ◽

2017 ◽

Vol 31 (34) ◽

pp. 1750326 ◽

Cited By ~ 1

Author(s):

Yefei Li ◽

Liang Sun ◽

Jiandong Xing ◽

Shengqiang Ma ◽

Qiaoling Zheng ◽

...

Keyword(s):

Electronic Structure ◽

Hydrostatic Pressure ◽

First Principles ◽

Density Functional ◽

Elastic Anisotropy ◽

Debye Model ◽

Mechanical Anisotropy ◽

Max Phase ◽

First Principles Calculations ◽

Covalent Bonds

First-principles calculations based on density functional theory (DFT) were used to investigate the mechanical properties, elastic anisotropy, electronic structure, optical properties and thermodynamic properties of a new quaternary MAX phase (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and its counterpart W[Formula: see text]AlC[Formula: see text] under hydrostatic pressure. The results indicate that the volumetric shrinkage of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] is faster than that of axial shrinkage under hydrostatic pressure. The stress–strain method and Voigt–Reuss–Hill approximation were used to calculate elastic constants and moduli, respectively. These compounds are mechanically stable under hydrostatic pressure. Moreover, the moduli of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] increase with an increase in pressure. The anisotropic indexes and surface constructions of bulk and Young’s moduli were used to illustrate the mechanical anisotropy under hydrostatic pressure. Electronic structure and optical property of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] have also been discussed. The results of Debye temperature reveal that the covalent bonds among atoms in (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] may be stronger than that of W3AlC[Formula: see text]. The heat capacity, [Formula: see text]–[Formula: see text], and thermal expansion coefficient of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] were discussed in the ranges of 0–30 GPa and 0–2000 K using quasi-harmonic Debye model considering the phonon effects.

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Interpretation of Valence Band X-Ray Spectra

Advances in X-ray Analysis ◽

10.1154/s0376030800011368 ◽

1969 ◽

Vol 13 ◽

pp. 182-236 ◽

Cited By ~ 8

Author(s):

David J. Nagel

Keyword(s):

Electronic Structure ◽

Valence Band ◽

Experimental Conditions ◽

X Ray ◽

Bonding Theory ◽

Spectral Interpretation ◽

Basic Work ◽

Band Spectra ◽

Valence Bands ◽

Basic Studies

X -ray spectra arising from the valence bands of solids are useful for basic studies of the electronic structure of most materials and for practical measurements of unknowns to obtain information on local atomic structure and material properties as well as chemical composition. Understanding the characteristics of valence band spectra is prerequisite to their fullest use. One-electron and many-body aspects of the x-ray emission process, and the effects of experimental conditions, must be understood and are reviewed. Interpretation of spectral features and determination of electronic structure are complementary parts of one procedure which is based on the use of bonding theory. The various band and bond theories which are finding use for spectral interpretation are briefly reviewed. Calculation of the electronic structure of aluminum metal and quartz, and interpretation of their x-ray spectra, are examples which illustrate basic work with valence band spectra.

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Electronic Structure of Metallophthalocyanines, MPc (M = Fe, Co, Ni, Cu, Zn, Mg) and Fluorinated MPc

10.26434/chemrxiv.13135676.v1 ◽

2020 ◽

Author(s):

Qunfei Zhou ◽

Zhen-Fei Liu ◽

Tobin J. Marks ◽

Pierre Darancet

Keyword(s):

Electronic Structure ◽

Density Functional ◽

Organometallic Compounds ◽

Optical Excitation ◽

Quantitative Agreement ◽

Excitation Energies ◽

Functional Theory ◽

Metal Phthalocyanines ◽

Optical Band Gaps ◽

Experimental Values

We compute the electronic structure and optical excitation energies of metal-free and transition metal phthalocyanines (H2Pc and MPc for M = Fe, Co, Ni, Cu, Zn, Mg) using density functionaltheory with optimally-tuned range-separated hybrid functionals (OT-RSH).We show that the OT-RSH approach provides photoemission spectra in quantitative agreement with experimentsas well as optical band gaps within 10% of their experimental values, capturing the interplay of localized d-states and delocalized pi-pi* states for these organometallic compounds. We examine the tunability of MPcs and H2Pc through fluorination, resulting in quasi-rigid shifts of the molecular orbital energies by up to about 0.7 eV. Our comprehensive dataset provides a new computational benchmark for phthalocyanines molecules, significantly improving upon other density-functional-theory-based approaches.

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