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.

The absorption spectrum of Ag I in the vacuum ultraviolet

1978 ◽  
Vol 361 (1706) ◽  
pp. 379-398 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Synchrotron Radiation ◽  
Variational Method ◽  
Theoretical Prediction ◽  
Ab Initio ◽  
Absorption Spectra ◽  
Vacuum Ultraviolet ◽  
Rydberg Series ◽  
Hartree Fock ◽  
Doubly Excited

The absorption spectrum of Ag I between 550 Å and 1590 Å has been investigated by using synchrotron radiation as the source of continuum. Over 50 new transitions are reported, nearly all of which can be classified into Rydberg series due to excitation of one electron from the 4d subshell. Identifications are made by comparison with previous studies of the arc spectrum as well as with absorption spectra of related elements. Ab initio Hartree-Fock calculations have revealed the importance of treating 5s 5p 1 P based levels by a separate variational method. Doubly excited configurations are also found, but, in contrast to a previous theoretical prediction, double vacancy production within the 4d subshell is not found to be significant for Ag I.

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.

On the validity of the spectator electrons model in the 3d and 4s excitation spectra of Mn I

1979 ◽  
Vol 367 (1730) ◽  
pp. 381-394 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Rydberg Series ◽  
Excitation Spectra ◽  
Hartree Fock ◽  
The Spectator

New observations of the absorption spectrum of Mn I between 1800 and 700 Å have revealed 77 new transitions, arrangeable in Rydberg series converging on to experimentally known levels of the ion. The analysis of the spectrum at wavelengths shorter than 1300 Å suggests assignments for several previously unidentified transitions in the 1300-1600 Å range. Comparisons with ah initio Hartree-Fock calculations are attempted, and the spectator electrons model is shown to provide the correct framework for the analysis of 3d and 4s excitation in Mn I.

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.

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.

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.

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.

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.

Single and double excitation spectra involving the 4d subshell of Ag I

1979 ◽  
Vol 365 (1721) ◽  
pp. 253-265 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Ab Initio ◽  
Detailed Analysis ◽  
Experimental Technique ◽  
Excitation Spectra ◽  
Double Excitation ◽  
Hartree Fock

Considerable extensions of the 4d-absorption spectrum of Ag I have resulted from improvements in experimental technique. All the allowed transitions to 4d 9 5s 5p have now been accounted for, and the weak n f series converging on the 4d 9 5s limits have been observed. Double excitations involving the 4d subshell have been detected. A detailed analysis is attempted by comparison with ab initio Hartree–Fock calculations.

Ab initio Hartree-Fock Investigation of π-Conjugated Compounds Presenting Large βv/βe Ratio: Merocyanines

1998 ◽  
Vol 63 (9) ◽  
pp. 1295-1308 ◽  
Author(s):  
Benoît Champagne ◽  
Thierry Legrand ◽  
Eric A. Perpete ◽  
Olivier Quinet ◽  
Jean-Marie André
Keyword(s):  
Ab Initio ◽  
First Hyperpolarizability ◽  
Conjugated Molecules ◽  
Hartree Fock ◽  
Experimental Discovery ◽  
Conjugated Compounds ◽  
Molecular Frame

CHF/6-311G* calculations of the first electronic and vibrational hyperpolarizabilities reveal that merocyanines present a substantial βv/βe ratio under their quinonoid nonpolar form. It originates from a large vibrational first hyperpolarizability whereas its electronic counterpart is small for this class of push-pull π-conjugated molecules. The transition from the quinonoid to the aromatic configuration is accompanied by an increase of βe and a decrease of the βv/βe ratio as well as by a ≈ 180° rotation in the plane of the molecule of βe and βv with respect to the molecular frame. Our results support the recent experimental discovery that antiparallel aggregation of aromatic and quinonoid forms of merocyanine is energetically favoured and that their first hyperpolarizabilities, which combine constructively, present both electronic and non purely electronic origins.

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