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  • American Institute of Physics (AIP)  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Use of canonical orbital energy derivatives for closed-shell self-consistent-field wave functions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 8749-8760 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The characteristics of the first and second derivatives of the canonical orbital energies for the closed shell self-consistent-field (SCF) wave function have been studied. The first derivatives of the orbital energies were determined analytically and the second derivatives by the finite difference method. These derivatives were transformed from the Cartesian coordinate system to the normal coordinate system for a variety of stationary points. It is demonstrated that the first and second derivatives of the orbital energies in terms of the normal coordinates provide very useful chemical information concerning the molecular structures and unimolecular reactions for a range of chemical species. Similarities and differences between the present approach and Mulliken–Walsh method are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464483
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  • 2
    Electronic Resource
    Electronic Resource
    The anharmonic potential function of methylene fluoride. SCF ab initio computations of the cubic force field and analysis of vibration–rotation interaction constants (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 959-967 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The harmonic and the cubic force fields of CH2F2 have been evaluated ab initio from the SCF energy expression by analytic derivative methods. The computed cubic force constants were used as starting values in a least squares analysis of the experimental vibration–rotation constants of CH2F2 and CD2F2. A simple scaling procedure of the ab initio cubic force constants provides a complete cubic force field for the molecule and the best fit with the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455165
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  • 3
    Electronic Resource
    Electronic Resource
    The molecular structure and vibrational spectrum of the cyclopropenyl cation, C3H+3, and its deuterated isotopomers (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4330-4340 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium structure, harmonic vibrational frequencies, infrared intensities, anharmonic constants, vibration–rotation interaction constants and quartic and sextic centrifugal distortion constants of C3H+3, the cyclopropenyl cation, and its deuterated isotopomers have been determined via purely ab initio quantum-mechanical methods. Two one-particle basis sets have been employed in conjunction with second-order M(approximately-equal-to)ller–Plesset perturbation theory (MP2), singles and doubles configuration interaction (CISD), and singles and doubles coupled cluster (CCSD). The best estimate of the harmonic frequencies is obtained from MP2 with a triple zeta plus double polarization (TZ2P) basis set. The anharmonic analysis has been determined via second-order perturbation theory using a double zeta plus polarization (DZP) self-consistent-field (SCF) full quartic force field. A generalization of formulas for the anharmonic analysis of D3h symmetric tops is discussed. The complete quartic force field in symmetry internal coordinates is given. Additionally, the anharmonic constants, vibration–rotation interaction constants and quartic and sextic centrifugal distortion constants for C3H+3 and C3D+3 are reported. Predictions of the fundamental vibrational frequencies for C3H+3 and all its deuterated isotopomers are reported. At the TZ2P MP2 level of theory the equilibrium structure of cyclopropenyl cation is Re(C–C)=1.3647 A(ring), Re(C–H)=1.0753 A(ring). Coupling the TZ2P MP2 harmonic frequencies with the DZP SCF anharmonic corrections, the infrared active fundamentals of C3H+3 are predicted to occur at 3136, 1289, 939, and 773 cm−1, with those of C3D+3 predicted to occur at 2346, 1243, 684, and 567 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456644
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  • 4
    Electronic Resource
    Electronic Resource
    The H+5 potential energy hypersurface: Characterization of ten distinct energetically low-lying stationary points (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5072-5081 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio molecular electronic structure theory has been used in an attempt to characterize the low-lying stationary points on the H+5 potential energy hypersurface. Three distinct levels of theory have been used: the self-consistent-field (SCF) method, configuration interaction (CI) including all single and double excitations, and full configuration interaction. Four different basis sets were used: double zeta (DZ), double zeta plus polarization (DZP), an extended basis set designated H (6s2p/4s2p), and a second extended basis set designated H (8s3p/6s3p). The higher levels of theory are in agreement that the only minimum for H+5 is a C2v structure, with three other stationary points (of D2d, C2v, and D2h symmetries) lying less than 1 kcal/mol higher in energy. The predicted dissociation energy D0 is 5.5 kcal/mol, which is estimated to be about 1 kcal/mol less than the exact D0. Furthermore, there are six other stationary points lying less than 8 kcal/mol above the minimum. Vibrational frequencies, dipole moments, and infrared intensities for each of the ten stationary points have been predicted at several different levels of theory. From the perspective of quantum chemistry, the H+5 system is very attractive as a candidate for the study of the vibrational dynamics of weakly bound systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452650
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  • 5
    Electronic Resource
    Electronic Resource
    Generalization of analytic energy third derivatives for the RHF closed-shell wave function: Derivative energy and integral formalisms and the prediction of vibration–rotation interaction constants (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5132-5142 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The general restricted Hartree–Fock (RHF) closed-shell energy analytic third derivative method is presented together with details concerning its implementation and that of the derivative integral algorithm. The viability of the energy equation and the integral techniques are illustrated by calculations on water, hydrogen cyanide, and formaldehyde with double zeta (DZ), double zeta plus polarization (DZP), triple zeta (TZ), triple zeta plus polarization (TZP), and triple zeta plus two sets of polarization (TZ2P) basis sets. Cubic force constants in reduced normal coordinates are reported for these basis sets. The cubic force constants are then applied in the prediction of the vibration–rotation interaction constants αBr (B=A, B, C) for these molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451707
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular structures and energetics for the lowest triplet states of glyoxal (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1741-1745 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium geometries of the lowest three triplet states of trans glyoxal (HCOHCO) have been predicted at the self-consistent-field (SCF) level of theory using a double zeta plus polarization (DZ+P) basis set, designated C,O(9s5p1d/4s2p1d), H(4s1p/2s1p). Two of the molecular structures thus predicted differ radically from the known 1Ag ground state equilibrium geometry. The predicted relative energies of the three triplet states are notably altered when the effects of electron correlation are treated theoretically. Using configuration interaction (CI) including single and double excitations, the predicted adiabatic excitation energies are 23 000 (a˜ 3Au n→π*), 31 000 (3Bg n→π*), and 31 000 cm−1 (3Bu π→π*), when corrected for unlinked cluster effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449361
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  • 7
    Electronic Resource
    Electronic Resource
    Analytic Raman intensities from molecular electronic wave functions (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 531-532 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An analytic method for the evaluation of Ramanintensities from closed−shell self-consistent-field wave functions is presented. Predictioinsf or ethylenemolecule are also reported. (AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450121
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