Compton Profiles and Nature of Bonding in Tantalum Chalcogenides

2013 ◽  
Vol 209 ◽  
pp. 143-146
Author(s):  
K.C. Bhamu ◽  
Arvind Sharma ◽  
Asvin R. Jani ◽  
B.L. Ahuja
Keyword(s):  
Linear Combination ◽  
Density Functional ◽  
Valence Electron ◽  
Population Analysis ◽  
Theoretical Data ◽  
Hartree Fock ◽  
Line Shapes ◽  
Valence Electron Density ◽  
Γ Ray ◽  
Gaussian Orbitals

Abstract. We report the Compton profiles of tantalum chalcogenides (TaS2 and TaSSe) using Hartree–Fock and hybridization of Hartree–Fock and density functional theories within linear combination of atomic (Gaussian) orbitals. To interpret the theoretical data on Compton line shapes, we have measured the Compton profiles using our in-house 100 mCi 241Am γ-ray Compton spectrometer. To understand the relative nature of bonding, we have obtained the equal-valence-electron-density (EVED) profiles. The EVED profiles shows that charge in TaSSe is more localized than TaS2 in the bonding direction which confirms that TaSSe is more covalent than TaS2, which is in agreement with the Mulliken’s population analysis.

Compton Profile Study of Aluminium Nitride

2007 ◽  
Vol 62 (12) ◽  
pp. 703-710 ◽  
Author(s):  
Vimal Vyas ◽  
Yogesh Chandra Sharma ◽  
Vinod Purvia ◽  
Narayan Lal Heda ◽  
Yamini Sharma ◽  
...  
Keyword(s):  
Density Functional ◽  
Population Analysis ◽  
Theoretical Data ◽  
Aluminium Nitride ◽  
Compton Profile ◽  
Energy Bands ◽  
Functional Theory ◽  
Hartree Fock ◽  
Ionic Nature ◽  
Γ Rays

In this paper we report the ab-initio theoretical Compton profiles of aluminium nitride (AlN) in the framework of the Hartree-Fock, density functional theory and hybridization of Hartree-Fock to density functional theories using the CRYSTAL03 code. To compare our first ever theoretical data, we have also measured the isotropic Compton profile of AlN, using 59.54 keV γ -rays. The Hartree- Fock scheme-based Compton profile agrees better with the experiment than the other theories. The energy bands, density of states and Mulliken’s population analysis, using the CRYSTAL03 code, are also reported. Our band structure calculations show a large band gap, while Mulliken’s population analysis shows the ionic nature of bonding in AlN.

scholarly journals Benchmarking semiempirical, Hartree–Fock, DFT, and MP2 methods against the ionization energies and electron affinities of short- through long-chain [n]acenes and [n]phenacenes

2016 ◽  
Vol 94 (3) ◽  
pp. 251-258 ◽  
Author(s):  
Sierra Rayne ◽  
Kaya Forest
Keyword(s):  
Density Functional ◽  
Theoretical Data ◽  
Theory Model ◽  
Basis Set ◽  
Electron Affinities ◽  
Ionization Energies ◽  
Hartree Fock ◽  
Wide Range ◽  
High Level ◽  
Long Chain

Vertical and adiabatic ionization energies (IEs) and electron affinities (EAs) were calculated for the n = 1–10 [n]acenes using a wide range of semiempirical, Hartree–Fock, density functional, and second-order Moller–Plesset perturbation theory model chemistries. None of the model chemistries examined was able to accurately predict the IEs or EAs for both short- through long-chain [n]acenes, as well as for extrapolations to the polymeric limit, when compared to available experimental and benchmark theoretical data. Except for 6-31G(d), the choice of the basis set does not affect B3LYP results significantly. Analogous calculations using a suite of eight modern and (or) popular density functionals for the n = 1–10 [n]phenacenes revealed similar problems in estimating the IEs and EAs of these compounds, with the sole exception of the M062X functional for adiabatic IEs and potentially the APFD, B3LYP, and MN12SX functionals for adiabatic EAs. The poor IE/EA prediction performance for the parent [n]acenes and [n]phenacenes may extend to their substituted derivatives and heteroatom-substituted analogs. Consequently, caution should be exercised in the application of non-high-level calculations for estimating the IE/EA of these important classes of materials.

Comparison of Experimental and Theoretical Structure Amplitudes and Valence Charge Densities of GaAs

1998 ◽  
Vol 54 (3) ◽  
pp. 231-239 ◽  
Author(s):  
J. Stahn ◽  
M. Möhle ◽  
U. Pietsch
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Theoretical Data ◽  
Charge Densities ◽  
Hartree Fock ◽  
Structure Factors ◽  
Nearest Neighbours ◽  
Kinematic Limit ◽  
Order Of Magnitude ◽  
The One

The current best sets of X-ray structure amplitudes for GaAs, gallium arsenide, are completed by highly precise data recorded at 0.50 < sin θ/λ < 1.35 Å−1. For the strong reflections the required accuracy of ΔF/F ≤ 1% was realized by the use of Pendellösung measurements at λ = 0.30 Å, recording the integral intensities as a function of the effective thickness from ∼500 µm thick GaAs wafers. Additionally, several weak reflections were determined from their integral intensities within the kinematic limit at wavelengths λ = 0.3, 0.56 and 0.71 Å. From these data individual Debye–Waller factors for gallium and arsenic were determined using the model of independent spherical atoms [B Ga = 0.666 (4) and B As = 0.566 (4) Å2]. The extended set of experimental structure factors now available is compared with those obtained by ab initio solid-state Hartree–Fock (HF) and density functional (DF) calculations. Therefore, the theoretical data were adapted to room temperature using the experimentally evaluated Debye–Waller factors and the model mentioned above. The valence and difference charge densities obtained from experimental and theoretical data show the expected charge accumulation between nearest neighbours slightly shifted towards the arsenic site. The disagreement remaining between the experimental and theoretical data, on the one hand, and between those of both ab initio methods, on the other hand, are of the same order of magnitude.

Quantum Mechanical Study of Clean and H-Covered α-MoO3(100) Surface

2003 ◽  
Vol 02 (02) ◽  
pp. 245-256 ◽  
Author(s):  
A. Sayede ◽  
B. Khelifa ◽  
C. Mathieu ◽  
H. Aourag
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Population Analysis ◽  
Chemical Properties ◽  
Hydrogen Atoms ◽  
Mulliken Population ◽  
Hartree Fock ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
Local Electronic Structure

Structure and electronic properties of the α-MoO3(100) surface, as well as H adsorption on the α-MoO3(100) surface have been studied with periodic slab Hartree–Fock calculations. Gradient corrected density functional calculations have been performed in this study. The structure and electronic properties of the (100) surface are in agreement with experimental and previous theoretical results. Local electronic structure near the different surface oxygen sites are analyzed with Mulliken Population Analysis. The oxide is partially ionic and the symmetrically oxygens exhibit more ionic feature while the terminal oxygens are more covalent. Electrostatic potentials show broad negative minima above the terminal oxygen centers, which suggest that electrophilic adparticles, like H, resulting from surface reactions, will be attracted preferentially at these sites. The results of the H adsorption on the (100) surface are interpreted based on charge-transfer interactions between the surface and H species. It is found that terminal oxygen sites are the most stable binding site. Ionic relaxation of the α-MoO3(100) surface for the adsorption of hydrogen has no effect on the chemical properties and hydrogen atoms adsorbed favorably on the α-MoO3(100) surface at full coverage.

Electronic Structure and Compton Profiles of Tungsten

2008 ◽  
Vol 63 (10-11) ◽  
pp. 703-711 ◽  
Author(s):  
Babu Lal Ahuja ◽  
Ashish Rathor ◽  
Vinit Sharma ◽  
Yamini Sharma ◽  
Ashvin Ramniklal Jani ◽  
...  
Keyword(s):  
Band Structure ◽  
Density Functional ◽  
Theoretical Data ◽  
Surface Topology ◽  
Full Potential ◽  
Energy Bands ◽  
Functional Theory ◽  
Hartree Fock ◽  
Spin Polarized ◽  
Linearized Augmented Plane Wave

The energy bands, density of states and Compton profiles of tungsten have been computed using band structure methods, namely the spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) approach as well as the linear combination of atomic orbitals with Hartree-Fock scheme and density functional theory. The full potential linearized augmented plane wave scheme to calculate these properties and the Fermi surface topology (except the momentum densities) have also been used to analyze the theoretical data on the electron momentum densities. The directional Compton profiles have been measured using a 100 mCi 241Am Compton spectrometer. From the comparison, the measured anisotropies are found to be in good agreement with the SPR-KKR calculations. The band structure calculations are also compared with the available data.

Ab initio determination of the valence electron distribution in the average structure of the incommensurately modulated calaverite AuTe2

2001 ◽  
Vol 57 (5) ◽  
pp. 633-637 ◽  
Author(s):  
Razvan Caracas ◽  
Xavier Gonze
Keyword(s):  
Electron Density Distribution ◽  
Density Functional ◽  
Valence Electron ◽  
Electronic Band Structure ◽  
Chemical Bonds ◽  
Electronic Band ◽  
Functional Theory ◽  
Average Structure ◽  
Valence Electron Density

The valence-electron density distribution of the average structure of incommensurately modulated calaverite, AuTe2, has been computed using density-functional theory. High-density regions, centered around the Au and Te atoms, are not spheric, but present charge concentrations along the Au—Te and Te—Te bonds. The electronic band structure and its corresponding density of states reveal the presence of three electronic band groups, constituted mainly by Te 5s, Au 5d and hybrids of Te 6p + Au 6s + Au 5d orbitals. The electrons belonging to the last block are responsible for the chemical bonds.

Valence electron spectroscopy of inhomogeneous media

1992 ◽  
Vol 50 (2) ◽  
pp. 1150-1151
Author(s):  
A. Howie ◽  
D.W. McComb
Keyword(s):  
Specific Gravity ◽  
Loss Function ◽  
Electron Spectroscopy ◽  
Valence Electron ◽  
Peak Height ◽  
Loss Functions ◽  
Loss Peak ◽  
High Energies ◽  
Valence Electron Density ◽  
Electron Microscopist

The bulk loss function Im(-l/ε (ω)), a well established tool for the interpretation of valence loss spectra, is being progressively adapted to the wide variety of inhomogeneous samples of interest to the electron microscopist. Proportionality between n, the local valence electron density, and ε-1 (Sellmeyer's equation) has sometimes been assumed but may not be valid even in homogeneous samples. Figs. 1 and 2 show the experimentally measured bulk loss functions for three pure silicates of different specific gravity ρ - quartz (ρ = 2.66), coesite (ρ = 2.93) and a zeolite (ρ = 1.79). Clearly, despite the substantial differences in density, the shift of the prominent loss peak is very small and far less than that predicted by scaling e for quartz with Sellmeyer's equation or even the somewhat smaller shift given by the Clausius-Mossotti (CM) relation which assumes proportionality between n (or ρ in this case) and (ε - 1)/(ε + 2). Both theories overestimate the rise in the peak height for coesite and underestimate the increase at high energies.

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