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'ab initio Calculations' in keywords
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2000 (1)
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1Author    MohammadA. QtaitatRequires cookie*
 Title    Conformational Stability and Structural Determination of Vinyldichlorosilane by ab initio Calculations  
 Abstract    The Conformational stability and barriers of interconversion between the eis and gauche conformers of vinyldichlorosilane, CH 2 CHSiHCl 2 , have been studied using ab initio calculations employing the RHF/3-21G* and RHF/6-31G* basis sets. The eis conformer was found to be more stable than the gauche one by 45 cm" 1 (539 J/mol) and 140 cm" 1 (1.68 kJ/mol) from the RHF/3-21G* and RHF/6-31G* basis sets, respectively. Additionally, the structural parameters of both rotamers have been calculated. These results are compared with results of related molecules. 
  Reference    Z. Naturforsch. 54a, 503—506 (1999); received July 30 1999 
  Published    1999 
  Keywords    Conformational Stability, ab initio Calculations, Vinyldichlorosilane 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0503.pdf 
 Identifier    ZNA-1999-54a-0503 
 Volume    54 
2Author    P. Lazzeretti, M. Malagoli, R. ZanasiRequires cookie*
 Title    Use of Symmetry in Coupled Hartree-Fock Calculations of Non-linear Response Tensors in Molecules  
 Abstract    A new computational scheme for electric dipole hyperpolarizabilities has been devised within the coupled Hartree-Fock method. Only the projection of second-order perturbed orbitals onto the subspace spanned by unperturbed virtual orbitals is computed. The entire molecular symmetry is exploited to reduce computational effort: a reduced two-electron integral file containing only sym-metry-distinct matrix elements over the atomic basis functions is processed at each iteration. In addition, only symmetry-independent first-and second-order perturbed density matrices need to be calculated. An efficient computer program implementing the present approach has been developed. 
  Reference    Z. Naturforsch. 48a, 141—144 (1993); received September 23 1991 
  Published    1993 
  Keywords    Second hyperpolarizability, Ab initio calculation, Molecular symmetry 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0141.pdf 
 Identifier    ZNA-1993-48a-0141 
 Volume    48 
3Author    Andrea Gruß, MichaelC. Böhm, Joachim Schulte, Klaus-Peter DinseRequires cookie*
 Title    An ab initio Hartree-Fock Investigation of Endohedral Sc@C  
 Abstract    The electronic structure of endohedral Sc@C 82 with a C 82 cage of C 2v symmetry has been studied by ab initio Hartree-Fock (HF) calculations. The optimized position of Sc in the configuration of minimum energy is predicted to be on the two-fold axis of the fullerene cage. In the corresponding configuration Sc is above the center of a hexagon of site symmetry C 2 . This structure of C 2v symmetry is nearly degenerate with C s and C t structures with Sc slightly displaced from the center of the coordinated hexagon. The binding energy of the endohedral complex is larger than 3.55 eV. The ab initio HF data of the C 2v topoisomer of the fullerene unit are compared with new experimental findings and HF results derived for the 3(C 2) topoisomer of the C 82 cage. 
  Reference    Z. Naturforsch. 53a, 801—805 (1998); received June 12 1998 
  Published    1998 
  Keywords    Endohedral Fullerenes, Electronic Structure, ab initio Calculations 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0801.pdf 
 Identifier    ZNA-1998-53a-0801 
 Volume    53 
4Author    S. Antolinez, J. L. Alonso, H. Dreizler, E. Hentrop, D. H. SutterRequires cookie*
 Title    Trifluoroacetic Acid; r 0 -Structure, Partial Substitution Structure and Deuterium Nuclear Quadrupole Coupling Studied by Molecular Beam Microwave Fourier Transform Spectroscopy and by ab initio Calculations  
 Abstract    We report the assignment and analysis of all stable monosubstituted isotopomers of trifluoroacetic acid. The 13 C and 18 0 isotopomers were observed in natural abundance. The rotational constants and quartic centrifugal constants are presented. The rotational constants are used to derive a partial substitution structure and a complete ro structure for future comparison with the corresponding values in hydrogen bridged bimolecules containing trifluoroacetic acid as a subunit. The deuterium nuclear quadrupole coupling constants are derived from the hfs-splittings of low-J rotational transitions of the CF 3 COOD isotopomer. The results of ab initio quantum chemical calculations are presented, which were carried out to assist in the assignment of the rotational spectra of the isotopomers and for comparison with the experimental molecular parameters. 
  Reference    Z. Naturforsch. 54a, 524—538 (1999); received August 3 1999 
  Published    1999 
  Keywords    Microwave Spectroscopy, Structure, D-hfs, Vibrational Averaging, ab initio Calculations 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0524.pdf 
 Identifier    ZNA-1999-54a-0524 
 Volume    54 
5Author    J. Breidung, H. Bürger, M. Senzlobei^, W. ThielRequires cookie*
 Title    High Resolution FTIR Spectrum of Chlorofluoroethyne  
 Abstract    , FCCC1, below 1000 cm -1 . Analysis of the v v v v v s , 2v 4 , v A + v 5 and 2i/ 5 Bands, and ab initio Calculations High resolution infrared spectra of FCCC1 have been measured and analyzed by polynomial methods. In the region below 350 cm -1 , the analysis is straightforward and yields parameters for the V4 = 1 and = 1 states. Between 350 and 800 cm -1 there are strong anharmonic interactions in the 2v 5 /u 4 + u^lu^llu^ tetrad which have been unravelled with the use of a model that employs ab initio interaction constants. Observed and theoretically predicted wavenumbers are in excellent agreement for all bands studied. 
  Reference    Z. Naturforsch. 54a, 236—244 (1999); received December 2 1998 
  Published    1999 
  Keywords    Infrared Spectrum, High Resolution, Alkyne, Fermi Resonance, ab initio Calculations 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0236.pdf 
 Identifier    ZNA-1999-54a-0236 
 Volume    54 
6Author    ValentinP. Feshin, ElenaV. FeshinaRequires cookie*
 Title    Correlation between the 35 CI NQR Parameters of Chloro-containing Organic and Organometallic Compounds and the Results of ab initio Calculations  
 Abstract    The results of comparison of experimental 35 C1 NQR parameters for a great number of organic and organometallic compounds and estimated ones using ab initio calculations at the RHF/6-31G(d) level were systematized. The NQR frequency changes on going from one compound to another depend, in general, on the changes of populations of the CI atom p"-orbitals in these compounds and, first of all, of populations of their less diffuse parts. 
  Reference    Z. Naturforsch. 55a, 555—559 (2000); received December 15 1999 
  Published    2000 
  Keywords    ab initio Calculations, p-orbital Populations, 35 C1 NQR Frequency, Asymmetry Parameter, Chloro-containing Organic and Organometallic Compounds 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0555.pdf 
 Identifier    ZNA-2000-55a-0555 
 Volume    55