Direct-space analysis of the electronic structure of the YBa2Cu3O6 and YBa2Cu3O7 crystals

2002 ◽  
Vol 80 (3) ◽  
pp. 235-244 ◽  
Author(s):  
Fausto Cargnoni ◽  
Marco Scavini
Keyword(s):  
Electronic Structure ◽  
Specific Cell ◽  
Electron Localization ◽  
Superconducting Transition ◽  
Complementary Information ◽  
Superconducting Cuprates ◽  
Atomic Orbitals ◽  
Hartree Fock ◽  
Atomic Properties ◽  
Pseudopotential Calculations

The electronic structure of the YBa2Cu3O6 and YBa2Cu3O7 crystals is investigated by means of fully periodic-restricted Hartree–Fock LCAO (linear combination of atomic orbitals) pseudopotential calculations. To give a detailed description of the bonding and atomic properties of the materials studied we selected the quantum theory of atoms in molecules approach, and complementary information is obtained from the analysis of the electron localization function in specific cell regions. The main features of the YBa2Cu3O6 and YBa2Cu3O7 crystals' electron densities are detailed and compared with available experimental data. Since the superconducting transition requires oxidation of the YBa2Cu3O6 crystal, we focused on the electronic rearrangements related to the inclusion of oxygen. Cu–O planes, probably responsible for the superconducting transition, exhibit peculiar electronic properties.Key words: superconducting cuprates, electron density, ab initio calculations.

scholarly journals Electronic Structure and Momentum Density of BaO and BaS

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
R. Kumar ◽  
B. K. Sharma ◽  
G. Sharma
Keyword(s):  
Electronic Structure ◽  
Charge Transfer ◽  
Momentum Density ◽  
Compton Profile ◽  
Density Profiles ◽  
Compound Formation ◽  
Atomic Orbitals ◽  
Hartree Fock ◽  
Valence Electron Density ◽  
Electron Density Profiles

The electronic structure and electron momentum density distribution in BaO and BaS are presented using Compton spectroscopy. The first-ever Compton profile measurements on polycrystalline BaO and BaS were performed using 59.54 keV gamma-rays. To interpret the experimental data, we have computed the theoretical Compton profiles of BaO and BaS using the linear combination of atomic orbitals method. In the present computation, the correlation scheme proposed by Perdew-Burke-Ernzerhof and the exchange scheme of Becke were considered. The hybrid B3PW and Hartree-Fock based profiles were also computed for both compounds. The ionic configurations are performed to estimate the charge transfer on compound formation, and the present study suggests charge transfer from Ba to O and S atoms. On the basis of equal-valence-electron-density profiles, it is found that BaO is more ionic as compared to BaS.

Ab initio band theory approach to electron energy loss near edge structures

1988 ◽  
Vol 46 ◽  
pp. 506-507
Author(s):  
Xudong Weng ◽  
O.F. Sankey ◽  
Peter Rez
Keyword(s):  
Ab Initio ◽  
Local Density ◽  
Interpolation Method ◽  
Atomic Orbital ◽  
Plane Waves ◽  
Large Set ◽  
Theory Approach ◽  
Band Theory ◽  
Atomic Orbitals ◽  
Pseudopotential Calculations

Single electron band structure techniques have been applied successfully to the interpretation of the near edge structures of metals and other materials. Among various band theories, the linear combination of atomic orbital (LCAO) method is especially simple and interpretable. The commonly used empirical LCAO method is mainly an interpolation method, where the energies and wave functions of atomic orbitals are adjusted in order to fit experimental or more accurately determined electron states. To achieve better accuracy, the size of calculation has to be expanded, for example, to include excited states and more-distant-neighboring atoms. This tends to sacrifice the simplicity and interpretability of the method.In this paper. we adopt an ab initio scheme which incorporates the conceptual advantage of the LCAO method with the accuracy of ab initio pseudopotential calculations. The so called pscudo-atomic-orbitals (PAO's), computed from a free atom within the local-density approximation and the pseudopotential approximation, are used as the basis of expansion, replacing the usually very large set of plane waves in the conventional pseudopotential method. These PAO's however, do not consist of a rigorously complete set of orthonormal states.

Ab Initio Study of Electronic Structure of RDX Molecular Crystal

1992 ◽  
Vol 296 ◽  
Author(s):  
Guang Gao ◽  
Ravindra Pandey ◽  
A. Barry Kunz
Keyword(s):  
Electronic Structure ◽  
Hot Spots ◽  
Molecular Crystal ◽  
Perfect Crystal ◽  
Local Region ◽  
Molecular Cluster ◽  
Ab Initio Study ◽  
Hartree Fock ◽  
Cyclotrimethylene Trinitramine ◽  
Defective Crystal

AbstractAn embedded molecular cluster model is used to study the electronic structure of cyclotrimethylene trinitramine(RDX) molecular crystal. In this model, a molecular cluster describing a local region of the crystal is treated in the Hartree-Fock approximation. The embedding lattice is represented by multipoles that are determined quantum-mechanically. Cluster-lattice orthogonality is achieved by transforming canonical orbitals to orbitals which are localized on individual molecular sites by means of a self-consistent localization potential. Results for the free molecule and the perfect crystal demonstrate the domination of three N-NO2 groups on intermolecular properties. For the defective crystal, results show a significant distortion in the electronic structure caused by local deformations in the lattice that may account for the formation of hot spots.

Electronic structure of cubic BaTbO3 from first-principles pseudopotential calculations

2006 ◽  
Vol 84 (2) ◽  
pp. 115-120 ◽  
Author(s):  
G Y Gao ◽  
K L Yao ◽  
Z L Liu
Keyword(s):  
Electronic Structure ◽  
First Principles ◽  
Density Functional ◽  
First Principles Calculations ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Pseudopotential Calculations ◽  
Correlation Potential ◽  
Density Contour

First-principles calculations of the electronic structure are performed for cubic BaTbO3 using the plane-wave pseudopotential method within the framework of density functional theory and using the generalized gradient approximation for the exchange-correlation potential. Our calculations show that cubic BaTbO3 is metallic, and that this metallic character is mainly governed by the Tb 4f electrons and the hybridization between the Tb 5d and O 2p states. From the analysis of the density of states, band structure, and charge density contour, we find that the chemical bonding between Tb and O is covalent while that between Ba and TbO3 is ionic. PACS Nos.: 71.15.Mb, 71.20.-b

Use of a Lowest Intensity 241Am Compton Spectrometer for the Measurement of Directional Compton Profiles of ZnSe

2006 ◽  
Vol 61 (7-8) ◽  
pp. 364-370 ◽  
Author(s):  
Babu Lal Ahuja ◽  
Narayan Lal Heda
Keyword(s):  
Bond Length ◽  
Theoretical Calculations ◽  
The Other ◽  
Energy Bands ◽  
Electron Momentum ◽  
Atomic Orbitals ◽  
Hartree Fock ◽  
Self Consistent ◽  
Scattering Technique ◽  
Small Disc

In this paper we report on electron momentum densities in ZnSe using Compton scattering technique. For the directional measurements we have employed a newly developed 100 mCi 241Am Compton spectrometer which is based on a small disc source with shortest geometry. For the theoretical calculations we have employed a self-consistent Hartree-Fock linear combination of atomic orbitals (HF-LCAO) approach. It is seen that the anisotropy in the measured Compton profiles is well reproduced by our HF-LCAOcalculation and the other available pseudopotential data. The anisotropy in the Compton profiles is explained in terms of energy bands and bond length. - PACS numbers: 13.60.Fz, 78.70. Ck, 78.70.-g

GSA algorithm applied to electronic structure: Hartree-Fock-GSA method

2005 ◽  
Vol 103 (5) ◽  
pp. 493-499 ◽  
Author(s):  
M. D. de Andrade ◽  
K. C. Mundim ◽  
L. A. C. Malbouisson
Keyword(s):  
Electronic Structure ◽  
Hartree Fock
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