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  • American Institute of Physics (AIP)  (4)
  • 1995-1999  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Energies of C2H5O and C2H5O+ isomers (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3292-3300 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Gaussian-2 (G2) theoretical procedure, based on ab initio molecular orbital theory, is used to calculate the energies of C2H5O and C2H5O+ isomers. The ethoxy radical cation (CH3CH2O+) is found to have a 3A‘ ground state while the singlet state is predicted to be unstable to rearrangement. The G2 adiabatic ionization potential of ethoxy radical is 10.32 eV in good agreement with a new ionization potential reported by Ruscic and Berkowitz of 10.29±0.08 eV from photoionization studies. The 2-hydroxyethyl radical (CH2CH2OH) has three isomers of nearly equal energy (within 1.6 kcal/mol). No stable 2-hydroxyethyl cation was located as it collapses to either O-protonated oxirane or 1-hydroxyethyl cation. The G2 appearance potential of CH3CHOH+ from ethanol of 10.79 eV is in excellent agreement with the recent photoionization value of 10.801±0.005 eV. The α(C–H), β(C–H), and O–H bond dissociation energies of ethanol are 94.9, 101.9, and 104.6 kcal/mol, respectively. The G2 result for the O–H bond energy is in good agreement with experiment while the results for the other two bond energies suggest that the experimental values for these quantities may be low. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468640
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  • 2
    Electronic Resource
    Electronic Resource
    Gaussian-2 theory: Use of higher level correlation methods, quadratic configuration interaction geometries, and second-order Møller–Plesset zero-point energies (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4192-4200 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The performance of Gaussian-2 theory is investigated when higher level theoretical methods are included for correlation effects, geometries, and zero-point energies. A higher level of correlation treatment is examined using Brueckner doubles [BD(T)] and coupled cluster [CCSD(T)] methods rather than quadratic configuration interaction [QCISD(T)]. The use of geometries optimized at the QCISD level rather than the second-order Møller–Plesset level (MP2) and the use of scaled MP2 zero-point energies rather than scaled Hartree–Fock (HF) zero-point energies have also been examined. The set of 125 energies used for validation of G2 theory [J. Chem. Phys. 94, 7221 (1991)] is used to test out these variations of G2 theory. Inclusion of higher levels of correlation treatment has little effect except in the cases of multiply-bonded systems. In these cases better agreement is obtained in some cases and poorer agreement in others so that there is no improvement in overall performance. The use of QCISD geometries yields significantly better agreement with experiment for several cases including the ionization potentials of CS and O2, electron affinity of CN, and dissociation energies of N2, O2, CN, and SO2. This leads to a slightly better agreement with experiment overall. The MP2 zero-point energies gives no overall improvement. These methods may be useful for specific systems. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470658
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  • 3
    Electronic Resource
    Electronic Resource
    6-31G* basis set for atoms K through Zn (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1223-1229 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Medium basis sets based upon contractions of Gaussian primitives are developed for the third-row elements K through Zn. The basis functions generalize the 6-31G and 6-31G* sets commonly used for atoms up to Ar. They use six primitive Gaussians for 1s, 2s, 2p, 3s, and 3p orbitals, and a split-valence pair of three and one primitives for valence orbitals, which are 4s and 5p for atoms K and Ca, and 4s, 4p, and 3d for atoms Sc through Zn. A 6-31G* set is formed by adding a single set of Gaussian polarization functions to the 6-31G set. They are Cartesian d-functions for atoms K and Ca, and Cartesian f-functions for atoms Sc through Zn. Comparison with experimental data shows relatively good agreement with bond lengths and angles for representative vapor-phase metal complexes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476673
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  • 4
    Electronic Resource
    Electronic Resource
    The relativistic Dirac–Coulomb–Fock effect on atomization energies (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7123-7126 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used a second-order perturbation treatment of the Dirac–Coulomb–Hartree–Fock method to estimate relativistic contributions to energies in the G2/97 test set. The one-electron relativistic effect on atomization energies of molecules containing first- and second-row atoms nearly always reduces binding. When the relativistic corrections are included in G3 theory and assessed on the G2/97 test set, there is little change in overall performance. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478615
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