Crystal excitation: survey of many-electron Hartree-Fock calculations of self-trapped excitons in insulating crystals

1992 ◽  
Vol 341 (1661) ◽  
pp. 221-231 ◽  
Keyword(s):  
Electronic Structure ◽  
Alkali Halides ◽  
Oxide Materials ◽  
Theoretical Methods ◽  
Hartree Fock ◽  
Cluster Calculations ◽  
Quantum Cluster ◽  
Similarities And Differences

To model successfully the diversity of electronic structure exhibited by excitons in alkali halides and in oxide materials, it is necessary to use a variety or combination of theoretical methods. In this review we restrict our discussion to the results of embedded quantum cluster calculations. By considering the results of such studies, it is possible to recognize the general similarities and differences in detail between the various exciton models in these materials.

Hartree-Fock Cluster Computations for Ionic Crystals

1985 ◽  
Vol 63 ◽  
Author(s):  
J. M. Vail ◽  
R. Pandey
Keyword(s):  
Shell Model ◽  
Alkaline Earth ◽  
Optical Transition ◽  
Alkali Halides ◽  
Wave Functions ◽  
Ionic Crystals ◽  
Perfect Lattice ◽  
Hartree Fock ◽  
Quantum Cluster ◽  
Model Lattice

ABSTRACTThe ICECAP code is applied to charged and uncharged color centers in alkali halides and alkaline-earth oxides, to test the usefulness of complete-cation pseudopotentials for reproducing the cluster boundary conditions. The physical model includes consistency up to electrostatic octupole order between the Hartree-Fock cluster and the surrounding infinite shell-model lattice. The total energy of the system is determined variationally, including distortion and polarization of the cluster and lattice, and LCAO-MO gaussian-localized cluster wave functions. Electronic states with the lattice unrelaxed are also analysed, yielding color-center optical transition energies. Furthermore, consistency between quantum (cluster) and classical (shell-model) descriptions of the perfect lattice is tested.

Calculations of the Electronic Structure of Vacancies in a-Si:H

1992 ◽  
Vol 291 ◽  
Author(s):  
Ariel A. Valladares ◽  
L. Enrique Sansores
Keyword(s):  
Electronic Structure ◽  
Charge Density ◽  
Density Of States ◽  
Energy Gap ◽  
Local Density ◽  
Amorphous Solids ◽  
Local Density Of States ◽  
Hydrogen Atoms ◽  
Hartree Fock ◽  
Cluster Calculations

ABSTRACTThe electronic structure of random clusters has been used in the literature as representative of the electronic structure of random solids. In this work a calculation of the local density of states (LDOS) and charge density contours for clusters of the type XSi20H28 with X an Si atom, a vacancy or 4 hydrogen atoms, has been carried out. The method used was a pseudopotential SCF Hartree-Fock and the HONDO program. It is found that the generation of a vacancy in the center of the cluster (removal of the central Si atom), introduces p-like states in the energy gap of the LDOS for the region near the center of the cluster. The saturation of the dangling bonds of the vacancy with 4 hydrogen atoms removes the states within the gap. These results are also borne out by the charge density contours, thereby reinforcing the importance of amorphous cluster calculations in the understanding of the electronic structure of amorphous solids.

THE ADSORPTION AND BONDING OF H2S ON THE α-FeOOH(110) SURFACE

2007 ◽  
Vol 14 (02) ◽  
pp. 209-217 ◽  
Author(s):  
S. SIMONETTI ◽  
D. DAMIANI ◽  
A. JUAN ◽  
G. BRIZUELA
Keyword(s):  
Electronic Structure ◽  
Density Of States ◽  
Minimum Energy ◽  
Stable Configuration ◽  
Molecular Adsorption ◽  
Cluster Calculations

The electronic structure of H 2 S adsorbed on the goethite (110) surface has been studied by ASED-MO cluster calculations. We have studied both the perpendicular and the parallel H 2 S molecular adsorption on the FeOOH (110) surface. We have analyzed the adsorption configuration energies including rotation. The parallel species does not rotate during adsorption and corresponds to the most stable configuration. We have also studied the bonding contributions for the minimum energy configuration and the density of states plots.

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.

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