Ab Initio and Model Calculations on Different Phases of Zirconia

1995 ◽  
Vol 408 ◽  
Author(s):  
Uwe Schönberger ◽  
Mark Wilson ◽  
Michael W. Finnis
Keyword(s):  
Ab Initio ◽  
Monoclinic Phase ◽  
Equilibrium Structure ◽  
Orbital Method ◽  
Full Potential ◽  
Model Calculations ◽  
Hartree Fock ◽  
Temperature Equilibrium ◽  
Empirical Shell Model ◽  
Semi Empirical

AbstractIn order to get a better understanding of the energetics of ZrO2 (zirconia) ab initio calculations with the full potential linear muffin tin orbital method ( fp LMTO) have been performed on the tetragonal structure over a range of c/a and sublattice displacement. A new semi-empirical shell model is developed which makes use of Hartree-Fock calculations and includes compressible anions and quadrupolar distortions. The empirical model predicts energies for tetragonal distortion in agreement with the fp LMTO calculations. Furthermore, it enables us to understand why the seven-fold coordinated monoclinic phase is the low temperature equilibrium structure.

Relation between Magnetic, Spectroscopic and Structural Properties of Binuclear Copper(II) Complexes of Pentadentate Schiff-base Ligand, Semi-empirical and ab-initio Calculations

2003 ◽  
Vol 58 (5-6) ◽  
pp. 363-372 ◽  
Author(s):  
Y. Elerman ◽  
H. Kara ◽  
A. Elmali
Keyword(s):  
Ab Initio ◽  
Coupling Constants ◽  
Antiferromagnetic Coupling ◽  
X Ray Diffraction ◽  
Hartree Fock ◽  
Ligand Orbital ◽  
Rhf Calculations ◽  
The Difference ◽  
Semi Empirical

The synthesis and characterization of [Cu2(L1)(3,5 prz)] (L1=1,3-Bis(2-hydroxy-3,5-chlorosalicylideneamino) propan-2-ol) 1 and of [Cu2(L2)(3,5 prz)] (L2=1,3-Bis(2-hydroxy-bromosalicylideneamino) propan-2-ol) 2 are reported. The compounds were studied by elemental analysis, infrared and electronic spectra. The structure of the Cu2(L1)(3,5 prz)] complex was determined by x-ray diffraction. The magnetochemical characteristics of these compounds were determined by temperaturedependent magnetic susceptibility measurements, revealing their antiferromagnetic coupling. The superexchange coupling constants are 210 cm−1 for 1 and 440 cm−1 for 2. The difference in the magnitude of the coupling constants was explained by the metal-ligand orbital overlaps and confirmed by ab-initio restricted Hartree-Fock (RHF) calculations. In order to determine the nature of the frontier orbitals, Extended Hückel Molecular Orbital (EHMO) calculations are also reported.

Equilibrium Structure and Schottky Barriers at Eras/Gaas Interfaces

1997 ◽  
Vol 492 ◽  
Author(s):  
A. G. Petukhov ◽  
B. T. Hemmelman ◽  
W. R. L. Lambrecht
Keyword(s):  
Local Density ◽  
Equilibrium Structure ◽  
Schottky Barriers ◽  
Orbital Method ◽  
Full Potential ◽  
Face Centered Cubic ◽  
Erbium Arsenide ◽  
Self Energy ◽  
Ideal Situation ◽  
Face Centered

ABSTRACTThe equilibrium structures as well as the electronic Schottky barriers for (100) Erbium-Arsenide/Gallium-Arsenide (ErAs/GaAs) arsenic and gallium terminated interfaces have been determined by ab-initio calculations using the local-density approximation and a full-potential linear-muffin-tin-orbital method. In both cases the arsenic sublattice was chosen to be continuous across the interface in accordance with experiments on Rutherford backscattering channeling. Band structures, densities of states, and charge density distributions were also determined for the interfaces. The comparison of the total supercell energies reveals that the gallium terminated (chain) interface is more energetically stable than the arsenic terminated (shadow) interface. It also shows that the equilibrium interface separation for the arsenic terminated interface corresponds to an ideal structure when arsenic forms undistorted face-centered cubic lattice. The separation in the gallium terminated interface is quite substantial and is 60% larger than that of the ideal situation. The model also predicts that no buckling of the ErAs interface monolayer will occur for either structure. The computed Schottky barriers for holes (after a semi-empirical quasiparticle self-energy correction) are 0.6 eV for the chain interface and 0.4 eV for the shadow interface.

scholarly journals Density functional tight binding: values of semi-empirical methods in an ab initio era

2014 ◽  
Vol 16 (28) ◽  
pp. 14368-14377 ◽  
Author(s):  
Qiang Cui ◽  
Marcus Elstner
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Tight Binding ◽  
Empirical Methods ◽  
Functional Theory ◽  
Hartree Fock ◽  
Semi Empirical

Semi-empirical (SE) methods are derived from Hartree–Fock (HF) or Density Functional Theory (DFT) by neglect and approximation of electronic integrals.

Theoretical studies of model compounds of lathyrane-type diterpenes

2004 ◽  
Vol 82 (1) ◽  
pp. 11-18 ◽  
Author(s):  
Yukimasa Terada ◽  
Tomoo Matsuura ◽  
Yukari Mori ◽  
Shosuke Yamamura
Keyword(s):  
Ab Initio ◽  
Molecular Mechanics ◽  
Molecular Orbital ◽  
Theoretical Calculations ◽  
Membered Ring ◽  
Orbital Method ◽  
Methyl Groups ◽  
Molecular Orbital Method ◽  
Stable Conformation ◽  
Semi Empirical

The conformation of the 11-membered ring of the lathyrane skeleton has been investigated using NMR spectra and theoretical calculations. Some other skeletons, such as jatrophane, jatrapholane, and tigliane, seem to be derived from this framework, and the conformation is important in connection with the configuration of the resultant diterpenes. The conformation of lathyrane is principally defined by the orientation of the two methyl groups; namely, the methyl groups on C1 and C6 directed above or below the ring plane. Theoretical calculations revealed that the predominant conformation is altered depending on the oxygen functional groups on the ring. As far as the bond lengths, bond angles, and dihedral angles are concerned, all calculation methods afforded reasonable results. In contrast, as regards conformational stability, only the ab initio molecular orbital method (RHF/6-31G*) predicted the most stable conformation, consistent with NOE experiments. On the other hand, the stable conformations predicted by the ab initio method (RHF/STO-3G), the semi-empirical molecular orbital method (MOPAC(PM3)), and the molecular mechanics calculations (MM3) did not necessarily agree with the conformers suggested by the NOE experiments.Key words: ab initio MO, semi-empirical MO, molecular mechanics, 11-membered ring conformation, NOE.

Calculations of Perovskite Surface Relaxation

2000 ◽  
Vol 654 ◽  
Author(s):  
E. Heifets ◽  
E.A. Kotominc ◽  
R.I. Eglitisc ◽  
R.E. Cohen
Keyword(s):  
Thin Films ◽  
Surface Energy ◽  
Ab Initio ◽  
Shell Model ◽  
Electron Correlation ◽  
Surface Relaxation ◽  
Hartree Fock ◽  
Semi Empirical ◽  
Good Agreement ◽  
Correlation Corrections

AbstractThe (100) and (110) surface relaxations are calculated for SrTiO3 and BaTiO3 perovskite thin films by means of a semi-empirical shell model (SM) for different surface terminations. Our SM results for the (100) surface structure are in good agreement with our present ab initio Hartree-Fock calculations with electron correlation corrections, previous ab initio pseudopotential calculationsand LEED experiments. The surface energy for the Ba-, Sr-, TiO- terminated (110) surfaces is found much larger than that for the (100) one. In contrast, the surface energy for the asymmetric O-termination, where outermost O atoms are strongly on-plane displaced, is the lowest for all (110) terminations and thus the most stable.

The simplified ab initio method calculation of linear polarizability

1973 ◽  
Vol 26 (5) ◽  
pp. 921 ◽  
Author(s):  
RD Brown ◽  
GR Williams
Keyword(s):  
Ab Initio ◽  
Small Molecules ◽  
Basis Set ◽  
Basis Sets ◽  
Orbital Method ◽  
Polarizability Anisotropy ◽  
Minimal Basis ◽  
Hartree Fock ◽  
Numerical Performance ◽  
Experimental Values

The simplified ab-initio molecular-orbital method described previously is particularly suited to the calculation of polarizabilities by the non-perturbative coupled Hartree-Fock technique. Trial calculations on CO and HF, for which comparison with corresponding ab-initio calculations is possible, show that the method gives an adequate numerical performance. Minimal basis set calculations in general tend to give values that are considerably too low because of inadequate flexibility of the basis and this is the origin of the large discrepancy between theory and experiment, especially for small molecules. ��� Results are also reported for N2O and O3. For these larger systems the SAI results with minimal basis sets are noticeably nearer experimental values. The polarizability anisotropy for N2O is particularly well reproduced by the SAI method. �

Semi-Empirical Calculations and Measurements of Modified Carbocyanines Optical Properties

1997 ◽  
Vol 479 ◽  
Author(s):  
Daniel G. McLean ◽  
Paul Day ◽  
Zhiqiang Wang ◽  
Nansheng Tang ◽  
Weijie Su ◽  
...  
Keyword(s):  
Optical Properties ◽  
Excited State ◽  
Ab Initio ◽  
Electronic Spectra ◽  
Reasonable Agreement ◽  
Dipole Moments ◽  
Hartree Fock ◽  
Spectral Changes ◽  
Multiple Conformations ◽  
Semi Empirical

AbstractWe report semi-empirical calculations of modified 3,3'-diethylthiacyanine iodide (DTC1), 3,3'-diethylthiacarbocyanine iodide (DTC3) and 3,3'-diethylthiadicarbocyanine iodide (DTC5), particularly with halogen substitution at the meso position in the polymethine bridge. Primarily we investigate geometrical changes and infer spectral trends from the molecular orbital levels. The semi-empirical calculations for the unsubstituted DTC3 agree well with an ab initio Hartree-Fock result. In all molecules multiple conformations are examined. Significant changes in dipole moments are noted between the cis and trans forms. Calculated electronic spectra at the CI singles level are compared to the measured spectra with reasonable agreement. Halogenation effects show a rotation of the benzthiazole groups out of planarity. We draw conclusions about consequent effects on solubility and excited state spectral changes.

The Spectator electrons approximation in the 3d and 4s spectra of Cr I

1981 ◽  
Vol 378 (1775) ◽  
pp. 445-460 ◽  
Keyword(s):  
Synchrotron Radiation ◽  
Ab Initio ◽  
Detailed Analysis ◽  
Electron Accelerator ◽  
Rydberg Series ◽  
Hartree Fock ◽  
Background Continuum ◽  
The Spectator ◽  
Semi Empirical ◽  
Transmission Windows

The 3d and 4s photoabsorption spectra of Cr I have been observed by using the synchrotron radiation emitted by the Bonn 500 MeV electron accelerator as the source of background continuum. The resulting spectrum is unexpectedly simple, and this is explained within the spectator electrons approximation. The more intense transitions can be arranged in Rydberg series. A prominent series of transmission windows arises by double excitation. A detailed analysis is presented, supported by some ab initio Hartree-Fock calculations and also by comparison with the semi-empirical calculations of Roth (1970) which include mixing between all the (3d + 4s) 5 4p configurations.

Calculations of Surface Structure for SrTiO3 Perovskite

2001 ◽  
Vol 672 ◽  
Author(s):  
E. Heifetsa ◽  
R.I. Eglitisb ◽  
E.A. Kotomin ◽  
G. Borstelb
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Dipole Moments ◽  
Surface Relaxation ◽  
Surface Layers ◽  
Functional Theory ◽  
Near Surface ◽  
Hartree Fock ◽  
Semi Empirical

ABSTRACTWe present and discuss results of the calculations for SrTiO3 (100) surface relaxation with different terminations (SrO and TiO2) using a semi-empirical shell model (SM) as well as abinitio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surfaceinduced dipole moments (polarization) for different terminations. We also compare results of the ab initio calculations based on both HF with the DFT-type electroncorrelation corrections, several DFT with different exchange-correlation functionals, and hybrid exchange techniques. OurSM results for the (100) surfaces are in a good agreement with both our ab initio calculations and LEED experiments.

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