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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio second- and fourth-order Møller–Plesset study on structure, stabilization energy, and stretching vibration of benzene⋅⋅⋅X (X=He,Ne,Ar,Kr,Xe) van der Waals molecules (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 335-340 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The C6v structure of benzene⋅⋅⋅X (X=He, Ne, Ar, Kr, Xe) complexes was investigated with second-order Møller–Plesset (MP2) theory; for the benzene⋅⋅⋅He the whole potential-energy surface (PES) was also studied. The stabilization energy of the benzene⋅⋅⋅He was also determined at the fourth-order Møller–Plesset (MP4) level; the respective MP4 stabilization energy is almost identical with MP2 stabilization energy which is due to the compensation of MP3 and MP4 contributions. The ab initio MP2 intermolecular distances agree nicely for all the complexes studied with the experimental value. While the stabilization energy of benzene⋅⋅⋅He and benzene⋅⋅⋅Ne (67 cm−1; 99 cm−1) is considerably smaller than that of benzene⋅⋅⋅Ar (429 cm−1), the intersystem distance differs less (3.32 A(ring), 3.50 A(ring), 3.53 A(ring)). The stabilization energies and intersystem distances for benzene⋅⋅⋅Kr and benzene⋅⋅⋅Xe are 485 and 601 cm−1 and 3.71 and 3.89 A(ring), respectively. The PES of benzene⋅⋅⋅He differs from that of benzene⋅⋅⋅Ar and can be characterized as more isotropic. The harmonic and anharmonic stretching frequencies were determined for all the complexes; anharmonicity plays a crucial role only for the benzene⋅⋅⋅He complex. Theoretical and experimental stretching frequencies for benzene⋅⋅⋅Ar and benzene⋅⋅⋅Kr agree very well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463578
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  • 2
    Electronic Resource
    Electronic Resource
    On the use of divergent series in vibrational spectroscopy. Two- and three-dimensional oscillators (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7331-7336 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Prospects for higher order perturbation theory in evaluating accurate eigenvalues and eigenvectors of the vibrational Hamiltonian are investigated by performing calculations on a series of two- and three-dimensional quartic anharmonic oscillators imitating vibrational motions in the H2O, H2S, NO2, SO2, and HOF triatomic molecules. Despite the fact that most of the corresponding perturbation expansion series diverge strongly they can be summed efficiently using the same methods as in previous studies on one-dimensional oscillators. Hence, higher order perturbation theory appears as a reasonable alternative to accurate variational methods in the case of small molecular systems and as a very promising tool for a proper treatment of larger systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465714
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  • 3
    Electronic Resource
    Electronic Resource
    Theory of hyperfine coupling constants of solvated molecules: Applications involving methyl and ClO2 radicals in different solvents (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 629-635 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A multiconfiguration self-consistent reaction field method is presented for calculating isotropic hyperfine coupling constants of solvated molecules. The solvent model is based on generalizations of Kirkwood's model for describing solvation effects. Isotropic hyperfine coupling constants are calculated for the methyl and ClO2 radicals in different solvents. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470858
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  • 4
    Electronic Resource
    Electronic Resource
    Ab initio calculations of anharmonic vibrational circular dichroism intensities of trans-2,3-dideuteriooxirane (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10548-10555 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A priori theory is derived for anharmonic calculations of vibrational circular dichroism (VCD). The anharmonic VCD expression is gauge origin independent and reduce to the magnetic field perturbation theory expression in the double-harmonic approximation. The theory has been implemented using second-order contact transformations for the vibration problem. Zeroth, first, and diagonal second derivatives of the atomic axial tensor are needed at the molecular equilibrium geometry. Ab initio calculations have been carried out for trans-2,3-dideuteriooxirane using self consistent field theory for the atomic axial tensors and using second-order Møller–Plesset theory for the atomic polar tensors and the force fields. The changes of the vibrational rotatory strengths from anharmonicities are small, and do not explain the previously observed large discrepancies between the double-harmonic results and the experimental values for three out of the 15 vibrational modes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469838
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  • 5
    Electronic Resource
    Electronic Resource
    Ab initio calculations of anharmonic vibrational transition intensities of trans-2,3-dideuteriooxirane (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10110-10115 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quartic force field and the cubic dipole moment surface are calculated for trans-2,3- dideuteriooxirane at the self-consistent field and the second order Möller–Plesset levels of theory using a triple zeta plus two polarization functions basis set. Contact transformation theory is used to determine the corresponding anharmonic vibrtional frequencies and intensities. Inclusion of anharmonicity improves agreement of the calculated frequencies and intensities with their experimental counterparts. The anharmonic corrections are much more sensitive to correlation effects for intensities than for frequencies. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470687
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  • 6
    Electronic Resource
    Electronic Resource
    Solution of the One-Dimensional Schroedinger Equation by the Combined Use of Symbolic and Numerical Computation (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 15608-15610 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100042a041
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  • 7
    Electronic Resource
    Electronic Resource
    Amino groups in nucleic acid bases, aniline, aminopyridines, and aminotriazine are nonplanar: Results of correlated ab initio quantum chemical calculations and anharmonic analysis of the aniline inversion motion (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 11042-11050 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The amino group nonplanarity in nucleic acid bases, aniline, aminopyridines, and aminotriazine was investigated by ab initio methods with and without inclusion of correlation energy utilizing medium and extended basis sets. For all the systems studied, the amino group was found to be nonplanar and the coupled cluster method [CCSD(T)] "nonplanarities'' and inversion barriers slightly higher than their second-order many-body perturbation-theory (MP2) counterparts. To assess the reliability of the calculations, inversion splittings for aniline and aniline-ND2 were evaluated by solving a two-dimensional vibrational Schrödinger equation for the large-amplitude inversion and torsion motions, while respecting the role of small-amplitude C–N stretching and H–N–H bending motions. Because a large number of points is required for the description of the aniline potential energy surface, the Hartree–Fock (HF) method with 6-31G* basis set was utilized. The vibrational calculations were performed within the framework of the semirigid bender Hamiltonian of Landsberg and Bunker. Excellent agreement between experimental and theoretical inversion-torsion frequencies for fundamental, overtone, and combination modes was found, which gives strong evidence for the adequacy of the theoretical model used in general, and potential energy surface in particular. Similarity between the HF, MP2, and CCSD(T) aniline inversion barriers and amino group nonplanarities gives us confidence that the MP2 and CCSD(T) inversion barriers and amino group nonplanarities of the DNA bases, aminopyridine, and aminotriazine, are close to the actual values which are still experimentally unknown. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472904
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  • 8
    Electronic Resource
    Electronic Resource
    Anharmonic treatment of the lowest-energy conformers of glycine: A theoretical study (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4629-4635 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure and energetics of the four lowest-energy conformers of glycine were determined at the MP2/aug-cc-pVDZ level of theory. The optimized structural parameters for these conformers agree with previous theoretical results obtained by highly correlated ab initio methods and with available experimental data. The only structure with planar heavy atom arrangement is conformer I (global minimum), the other conformers have nonplanar heavy atom arrangements. In accordance with temperature dependence studies of the vibrational spectra in various rare gas environments, conformers III and IV have small interconversion barriers to conformer I (940 and 740 cm−1). Our calculations have shown that full-dimensional anharmonic treatment is required for an accurate description of the vibrational modes in various glycine conformers. The most pronounced effect has been observed for conformer II with the intramolecular O–H⋅⋅⋅N bond. The theoretical results obtained at the MP2/aug-cc-pVDZ level reproduce quantitatively the argon matrix experiments. The calculation uses the quartic force field approximation in the framework of second-order perturbation theory. An estimate of the higher-order correction is also given. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288914
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  • 9
    Electronic Resource
    Electronic Resource
    Use of Gauss–Hermite quadrature in the treatment of predissociation resonances with the complex-scaling method (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 3014-3020 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An efficient numerical integration procedure based on the Gauss–Hermite quadrature is developed for evaluation of rovibrational Hamiltonian matrix elements in a basis of complex-scaled harmonic oscillator functions. By scaling the basis functions rather than the Hamiltonian itself, it is possible to employ molecular potential energy and coupling data directly in numerical form without first having to fit them to analytical functions. The new method is employed for the treatment of the CO B-D 1Σ+ system by employing model diabatic potentials and coupling elements from the literature. Calculations are carried out in both the original diabatic and the corresponding adiabatic representation of the electronic states. Because of the sharp oscillations in the nonadiabatic coupling functions it is found that the convergence properties in the diabatic basis are somewhat better than in the corresponding adiabatic treatment, but very good agreement is obtained between the two sets of energy and linewidth results for the lowest 11 vibrational states. Comparison is also made with earlier results for the same system obtained by employing the optical potential and close coupling methods, respectively. The second-derivative G12 coupling matrix elements are found to have an important effect on the computations in the adiabatic representation and are essential for obtaining a high level of agreement with the corresponding diabatic results. The present method is well-suited for applications based on ab initio potential energy surfaces and couplings since it requires neither that the pointwise computed data be fitted to polynomials nor that they be subjected to a diabatic transformation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474702
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  • 10
    Electronic Resource
    Electronic Resource
    Ab initio configuration interaction study of the predissociation of the (4s), (4pσ) 1,3Π, and (4pπ) 3Σ+ Rydberg states of HCl and DCl (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 260-267 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio configuration interaction (Cl) calculations are carried out for the lowest-lying six 1,3Π and three 3Σ+ states. In addition, the first and second radial couplings 〈φi(R,r)|∂/∂R|φj(R,r)〉 and 〈φi(R,r)|∂2/∂R2|φj(R,r)〉, spin-orbit, and rotational couplings are also evaluated based on the resulting highly correlated wave functions. Energy positions and predissociation linewidths of rovibrational levels associated with the above electronic states are determined in the adiabatic representation by means of the complex scaling method employing a basis of complex scaled Hermite polynomials and Gauss–Hermite quadrature. The present treatment correctly reproduces a number of observed trends in energy and line broadening for individual rovibrational levels of the (4s)b 3Π and C 1Π states of HCl and DCl. The calculated linewidths for the v=0, J=2, and J=8 rovibrational levels of the (4s)C 1Π state of HCl are 1.2 and 2.1 cm−1, respectively, which is in good agreement with the recently observed rotational dependence of line broadening for the v=0 level of this state [M. H. Alexander et al., Chem. Phys. 231, 331 (1998)]. The present calculations find that the linewidths of the (4pσ)D 1Π state are greater than for the (4pσ)d 3Π state. The distinctive predissociation mechanisms of the D 1Π and the d 3Π states are discussed on the basis of the calculated radial couplings. The calculations predict very broad lines for the v=0 and 1 vibrational levels of the lowest adiabatic bound 3Σ+ state, consistent with the fact that the corresponding state has not yet been identified by spectroscopic means. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480578
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