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  • AIP Publishing  (11)
  • 1965-1969  (11)
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  • AIP Publishing  (11)
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  • 1965-1969  (11)
Year
  • 1
    Online Resource
    Online Resource
    Internal Rotation Barriers for Hydrazine and Hydroxylamine from Ab Initio LCAO—MO—SCF Wavefunctions
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 47, No. 3 ( 1967-08-01), p. 895-905
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 47, No. 3 ( 1967-08-01), p. 895-905
    Abstract: LCAO—MO—SCF ab initio wavefunctions with atomic basis orbitals of double-zeta accuracy have been constructed for N2H4 and NH2OH and the potential-energy curves versus internal-rotation angle have been determined. Similar wavefunctions for CH3CH3, CH3OH, CH3NH2, and H2O2, reported previously, showed a quantitatively useful correlation with experimental barrier heights and shapes. Since experimental information on the N2H4 and NH2OH barriers is incomplete or unknown, the theoretical results presented here may help guide experimental work. Decomposition of the total energy into one- and two-electron components has been found previously to help elucidate the physical origin of the rotational barrier, and results for the species studied here are given. The wavefunctions presented here (and those reported previously for the species noted above) are the most accurate available for molecules possessing a rotational barrier about a single bond, and comparison is made with the results of the other existing ab initio wavefunctions.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1712054
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Electronic Structure and Geometry of Hydrogen Cyanide
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 5 ( 1967-03-01), p. 1797-1803
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 5 ( 1967-03-01), p. 1797-1803
    Abstract: The geometry and charge distribution of HCN in its ground state has been determined by means of many-electron, self-consistent-field molecular-orbital wavefunctions. LCAO MO SCF calculations and ones which split the AO's with linear variation coefficients yield properties and total energies reasonably close to the molecular Hartree—Fock limit. A linear molecule with bond distances correct to 1% of the microwave spectroscopy values is obtained. Walsh's orbital-energy diagrams are found to be almost independent of angle but with nearly compensating variations and for this molecule Walsh's orbital-energy summation criterion leads to a bent ground state. This result, however, is easily understood in terms of the relatively high ionic character of the H–CN bond. An empirical molecular bind energy correlation scheme based on diatomic molecular Hartree—Fock solutions is employed to analyze the difference between the computed (7.10 eV) and the experimental (13.53 eV) binding energy values.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1840937
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
    Online Resource
    Online Resource
    Numerical Test of the Integral Hellmann—Feynman Theorem
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 8 ( 1967-04-15), p. 3270-3271
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 8 ( 1967-04-15), p. 3270-3271
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1841204
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
    Online Resource
    Online Resource
    Origin of Rotational Barriers. II. Methylamine and Improved Wavefunctions for Hydrogen Peroxide
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 6 ( 1967-03-15), p. 2276-2284
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 6 ( 1967-03-15), p. 2276-2284
    Abstract: LC(Hartree—Fock) AO MO SCF wavefunctions have been constructed for CH3NH2 and MO SCF wavefunctions beyond this level of approximation for H2O2. Analysis of these solutions along with wavefunctions determined previously for CH3CH3 and CH3OH makes possible several conclusions concerning the origin of rotational barriers: (1) Study of a sequence of molecules, including particularly those of low symmetry, is required for detailed understanding. (2) The origin may be found within the framework of the Hartree—Fock approximation. (3) Decomposition of the total energy into one- and two-electron components elucidates the barrier origin and provides a physical picture of the barrier mechanism as a delicate balance between the interactions of lone pairs, bonds, and protons.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1841032
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 5
    Online Resource
    Online Resource
    Method for Computing Multicenter One- and Two-Electron Integrals
    AIP Publishing ; 1965
    In:  The Journal of Chemical Physics Vol. 43, No. 10 ( 1965-11-15), p. S170-S171
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 43, No. 10 ( 1965-11-15), p. S170-S171
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1701481
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1965
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 6
    Online Resource
    Online Resource
    Extended Hückel Theory and the Shape of Molecules
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 3 ( 1967-02-01), p. 1029-1037
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 3 ( 1967-02-01), p. 1029-1037
    Abstract: Ab initio MO SCF wavefunctions and one-electron energies are compared with extended-Hückel-theory values for the polyatomic molecules BeH2, BH2+, BH2−, NH2+, H2O, BeH3−, BH3, CH3+, Li2O, F2O, LiOH, and FOH. A remarkable similarity in the nodal structure, order of the energy levels, prediction of molecular shape, and changes in hybridization and ionization potential with angle is observed. The origin of this correspondence for molecular shape is found to be a general theorem relating changes in the sum of one-electron energies to the total energy and implying a low information content to the angular dependence of molecular energetics. Analysis of the Hückel molecular orbitals also shows that quantitative evaluation of many other chemically interesting quantities is not to be expected. These investigations help give a quantum-mechanical underpinning to extended Hückel theory, elucidate its a priori capabilities, and lead to proposals for realizing more quantitative predictions from this model.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1840764
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 7
    Online Resource
    Online Resource
    Theory of the Hydrogen Bond: Electronic Structure and Properties of the Water Dimer
    AIP Publishing ; 1969
    In:  The Journal of Chemical Physics Vol. 51, No. 8 ( 1969-10-15), p. 3286-3293
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 51, No. 8 ( 1969-10-15), p. 3286-3293
    Abstract: High-accuracy molecular-orbital calculations using essentially Hartree–Fock quality atomic orbitals as a basis have been carried out on different geometries of the water dimer. Different basis sets have been considered. The molecular-orbital approach is shown to well represent the geometry and heat of formation (− 5.3 kcal/mole) of the water dimer as well as general infrared spectral properties of the hydrogen bond. The individual molecular-orbital energies are shown to increase for the electron acceptor and to decrease for the electron donor. This trend in energies is proposed as a quantitative organizing principle for not only H-bond formation but all donor–acceptor interactions.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1672509
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1969
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 8
    Online Resource
    Online Resource
    Geometry of Molecules. I. Wavefunctions for Some Six- and Eight-Electron Polyhydrides
    AIP Publishing ; 1966
    In:  The Journal of Chemical Physics Vol. 45, No. 2 ( 1966-07-15), p. 734-749
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 45, No. 2 ( 1966-07-15), p. 734-749
    Abstract: Potential surfaces have been investigated for BH2+, BH2−, NH2+, BeH2, BH3, CH3+, and BeH3− by means of LC (Hartree—Fock) AO MO SCF wavefunctions. One-electron-energy-versus-angle diagrams were determined for these AH2 and AH3 molecules, and comparison with the widely used empirical diagrams of Walsh demonstrates a quantitative similarity between them. In addition, mathematical inequalities are derived relating changes in the sum of one-electron energies with angle to changes in the total energy with angle. Aided by these expressions, we are able to make direct connection between Walsh's qualitative rules and the physically well-defined ab initio solutions.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1727634
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1966
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 9
    Online Resource
    Online Resource
    Geometry of Molecules. II. Diborane and Ethane
    AIP Publishing ; 1966
    In:  The Journal of Chemical Physics Vol. 45, No. 8 ( 1966-10-15), p. 2835-2847
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 45, No. 8 ( 1966-10-15), p. 2835-2847
    Abstract: The diborane molecule has been investigated in its equilibrium D2h geometry, in the D3d (ethane) structure, and three intermediate configurations. Charge-contour diagrams show that the electron distribution between the boron nuclei is considerably less concentrated than in the boron—bridge-hydrogen bonds. Calculations for ethane in both equilibrium and bridged-hydrogen configurations show that the carbon p functions of C2H6 play a much greater role in molecular binding than those of boron in B2H6 and this fact explains their different geometry.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1728036
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1966
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 10
    Online Resource
    Online Resource
    Origin of Rotational Barriers. I. Many-Electron Molecular Orbital Wavefunctions for Ethane, Methyl Alcohol, and Hydrogen Peroxide
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 6 ( 1967-03-15), p. 2261-2275
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 6 ( 1967-03-15), p. 2261-2275
    Abstract: An investigation into the origin of rotation barriers has been carried out with the aid of LC(Hartree—Fock) AO MO SCF calculations on CH3CH3, CH3OH, and H2O2. The general shape and magnitudes of the barriers are reasonably well represented by the wavefunctions and one may conclude that the origin of rotational barriers is to be found within the framework of the Hartree—Fock approximation. It is also found that study of several molecules, particularly ones of low symmetry, is required for a detailed understanding of barriers. The electronic energy has been decomposed into one- and two-electron parts. The relative phase and relative amplitude of these two components provide the best invariants available for analyzing the barrier mechanism. On the other hand the nuclear—nuclear repulsion is shown not to be an appropriate invariant. A physical picture of the barrier mechanism constructed from the electronic-energy decomposition depicts the barrier origin as a balance between the interactions of lone pairs, bonds, and the protons.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1841031
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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