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  • 1
    Electronic Resource
    Electronic Resource
    From Intermolecular Potentials to the Spectra of van der Waals Molecules, and Vice Versa (1994)
    s.l. : American Chemical Society
    Chemical reviews 94 (1994), S. 1931-1974 
    Details
    ISSN: 1520-6890
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cr00031a009
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  • 2
    Electronic Resource
    Electronic Resource
    Perturbation Theory Approach to Intermolecular Potential Energy Surfaces of van der Waals Complexes (1994)
    s.l. : American Chemical Society
    Chemical reviews 94 (1994), S. 1887-1930 
    Details
    ISSN: 1520-6890
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cr00031a008
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopic, collisional, and thermodynamic properties of the He–CO2 complex from an ab initio potential: Theoretical predictions and confrontation with the experimental data (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 3074-3084 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Symmetry-adapted perturbation theory has been applied to compute the intermolecular potential energy surface of the He–CO2 complex. The ab initio potential has a global minimum of εm=−50.38 cm−1 at Rm=5.81 bohr for the "T"-shaped geometry of the complex, and a local one of εm=−28.94 cm−1 at Rm=8.03 bohr for the linear He⋅⋅⋅O(Double Bond)C(Double Bond)O structure. The computed potential energy surface has been analytically fitted and used in converged variational calculations to generate bound rovibrational states of the He–CO2 complex and the infrared spectrum corresponding to the simultaneous excitation of the ν3 vibration and internal rotation in the CO2 subunit within the complex. The complex was shown to be a semirigid asymmetric top and the rovibrational energy levels could be classified with the asymmetric top quantum numbers. The computed frequencies of the infrared transitions in the ν4 band of the spectrum are in very good agreement with the high resolution experimental data of Weida et al. [J. Chem. Phys. 101, 8351 (1994)]. The energy levels corresponding to the ν5 bending mode of the complex have been used to compute the transition frequencies in the ν5 hot band of He–CO2. A tentative assignment of the transitions observed in the ν5 band with the quantum numbers of the asymmetric rotor is presented. As a further test of the ab initio potential we also report the pressure broadening coefficients of the R branch rotational lines of the ν3 spectrum of CO2 in a helium bath at various temperatures. Very good agreement is found with the wealth of experimental results for various rotational states of CO2 at different temperatures. Finally, we also tested the potential by computing the second virial coefficients at various temperatures. Again, the agreement between theory and experiment is satisfactory, showing that the ab initio potential can reproduce various physical properties of the complex. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1385524
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  • 4
    Electronic Resource
    Electronic Resource
    Many-body theory of exchange effects in intermolecular interactions. Second-quantization approach and comparison with full configuration interaction results (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1312-1325 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Explicitly connected many-body perturbation expansion for the energy of the first-order exchange interaction between closed-shell atoms or molecules is derived. The influence of the intramonomer electron correlation is accounted for by a perturbation expansion in terms of the Møller–Plesset fluctuation potentials WA and WB of the monomers or by a nonperturbative coupled-cluster type procedure. Detailed orbital expressions for the intramonomer correlation corrections of the first and second order in WA+WB are given. Our method leads to novel expressions for the exchange energies in which the exchange and hybrid integrals do not appear. These expressions, involving only the Coulomb and overlap integrals, are structurally similar to the standard many-body perturbation theory expressions for the polarization energies. Thus, the exchange corrections can be easily coded by suitably modifying the existing induction and dispersion energy codes. As a test of our method we have performed calculations of the first-order exchange energy for the He2, (H2)2, and He–H2 complexes. The results of the perturbative calculations are compared with the full configuration interaction data computed using the same basis sets. It is shown that the Møller–Plesset expansion of the first-order exchange energy converges moderately fast, whereas the nonperturbative coupled-cluster type approximations reproduce the full configuration interaction results very accurately.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466661
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  • 5
    Electronic Resource
    Electronic Resource
    Intermolecular potential and rovibrational levels of Ar–HF from symmetry-adapted perturbation theory (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6076-6092 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A two-dimensional intermolecular potential energy surface for Ar–HF has been calculated using the many-body symmetry-adapted perturbation theory (SAPT). The H–F distance was kept constant at its equilibrium value. The interaction energies have been computed using an spdfg-symmetry basis optimized for intermolecular interactions. In addition, the dispersion and induction energies have been calculated in a few progressively larger basis sets to determine the basis set convergence and validity of the asymptotic scaling of those components. Converged results for the dispersion energy have been obtained by using a large basis set containing spdfgh-symmetry orbitals. The ab initio SAPT potential agrees well with the empirical H6(4,3,2) potential of Hutson [J. Chem. Phys. 96, 6752 (1992)], including a reasonably similar account of the anisotropy. It predicts an absolute minimum of −207.4 cm−1 for the linear Ar–HF geometry at an intermolecular separation of 6.53 bohr and a secondary minimum of −111.0 cm−1 for the linear Ar–FH geometry at an intermolecular separation of 6.36 bohr. The corresponding values for the H6(4,3,2) potential are −211.1 cm−1 at an intermolecular separation of 6.50 bohr and −108.8 cm−1 at an intermolecular separation of 6.38 bohr. Despite this agreement in the overall potentials, the individual components describing different physical effects are quite different in the SAPT and H6(4,3,2) potentials. The SAPT potential has been used to generate rovibrational levels of the complex which were compared to the levels predicted by H6(4,3,2) at the equilibrium separation. The agreement is excellent for stretch-type states (to within 1 cm−1), while states corresponding to bending vibrations agree to a few cm−1. The latter discrepancies are consistent with the differences in anisotropies of the two potentials. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470436
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  • 6
    Electronic Resource
    Electronic Resource
    Dispersion energy in the coupled pair approximation with noniterative inclusion of single and triple excitations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4586-4599 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The second-order dispersion energy in the coupled-pair (coupled-cluster doubles) approximation has been derived. The coupled-pair amplitudes are subsequently used in a perturbation theory type expression to account for the effects of single and triple excitations. This approach selectively sums to infinite order important classes of intramonomer correlation diagrams resulting in a better theoretical description of the dispersion interaction compared to a finite-order perturbation treatment. Numerical results have been obtained for He2, Ar–H2, Ar–HF, (HF)2, (H2O)2, and He–F− in various geometries and basis sets to illustrate the performance of the nonperturbative versus perturbative treatments of the intramonomer correlation contributions to the energy of the dispersion interaction. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470646
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  • 7
    Electronic Resource
    Electronic Resource
    Ab initio potential energy surface, infrared spectrum, and second virial coefficient of the He–CO complex (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 321-332 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Symmetry-adapted perturbation theory has been applied to compute the intermolecular potential energy surface of the He–CO complex. The interaction energy is found to be dominated by the first-order exchange contribution and the dispersion energy. The ab initio potential has a single minimum of εm=−24.895 cm−1 for the linear CO–He geometry at Rm=6.85 bohr. The computed potential energy surface has been analytically fitted and used in converged variational calculations to generate bound rovibrational states of the He–CO molecule and the infrared spectrum, which corresponds to the simultaneous excitation of vibration and internal rotation in the CO subunit within the complex. The predicted positions and intensities of lines in the infrared spectrum are in good agreement with the experimental spectrum [C.E. Chuaqui et al., J. Chem. Phys. 101, 39 (1994)]. The theoretical potential was also checked by comparison of computed excess second virial coefficients with the experimental data. The ab initio interaction virial coefficients, including quantum corrections, lie within the experimental error bars over a wide range of temperatures. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469644
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio potential energy surface and near-infrared spectrum of the He–C2H2 complex (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8385-8397 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Symmetry-adapted perturbation theory has been applied to compute the intermolecular potential energy surface of the He–C2H2 complex. The interaction energy is found to be dominated by the first-order exchange contribution and the dispersion energy. In both contributions it was necessary to include high-level intramolecular correlation effects. Our potential has a global minimum of εm=−22.292 cm−1 near the linear He–HCCH geometry at Rm=8.20 bohr and cursive-thetam=14.16°, and a local minimum at a skew geometry (Rm=7.39 bohr, cursive-thetam=48.82°, and εm=−21.983 cm−1). The computed potential energy surface has been analytically fitted and used in converged variational calculations to generate bound rovibrational states of the He–C2H2 molecule and the near-infrared spectrum, which corresponds to the simultaneous excitation of the vibration and hindered rotation of the C2H2 monomer within the complex. The nature of the bound states and of the spectrum predicted from the ab initio potential are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468830
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  • 9
    Electronic Resource
    Electronic Resource
    Symmetry-adapted perturbation theory of nonadditive three-body interactions in van der Waals molecules. I. General theory (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8058-8074 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Symmetry-adapted perturbation theory of pairwise nonadditive interactions in trimers is formulated, and pure three-body polarization and exchange components are explicitly separated out. It is shown that the three-body polarization contributions through the third order of perturbation theory naturally separate into terms describing the pure induction, mixed induction–dispersion, and pure dispersion interactions. Working equations for these components in terms of molecular integrals and linear and quadratic response functions are derived. These formulas have a clear, partly classical, partly quantum mechanical, physical interpretation. The asymptotic expressions for the second- and third-order three-body polarization contributions through the multipole moments and (hyper)polarizabilities of the isolated monomers are reported. Finally, assuming the random phase approximation for the response functions, explicit orbital formulas for the three-body polarization terms are derived. The exchange terms are also classified, and the simplest approximations (neglecting intramonomer correlation effects) are written as explicitly connected commutator expressions involving second-quantized operators. The corresponding orbital formulas are also reported. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470171
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  • 10
    Electronic Resource
    Electronic Resource
    Near-infrared spectrum and rotational predissociation dynamics of the He–HF complex from an ab initio symmetry-adapted perturbation theory potential (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2825-2835 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Starting from an ab initio symmetry-adapted perturbation theory potential energy surface we have performed converged variational and close-coupling calculations of the bound rovibrational states and of the positions and widths of rotationally predissociating resonances of HeHF and HeDF van der Waals complexes. The energy levels were used to compute transition frequencies in the near-infrared spectra of these complexes corresponding to the simultaneous excitation of vibration and internal rotation in the HF(DF) subunit in the complex. The computed transition energies and other model independent characteristics of the near-infrared spectra are in excellent agreement with the results of high-resolution measurements of Lovejoy and Nesbitt [C. M. Lovejoy and D. J. Nesbitt, J. Chem. Phys. 93, 5387 (1990)]. In particular, the ab initio potential predicts dissociation energies of 7.38 and 7.50 cm−1 for HeHF and HeDF, respectively, in very good agreement with the Lovejoy and Nesbitt results of 7.35 and 7.52 cm−1. The agreement of the observed and calculated linewidths is less satisfactory. We have found, however, that the linewidths are very sensitive to the accuracy of the short-range contribution to the V1(r,R) term in the anisotropic expansion of the potential. By simple scaling of the latter component we have obtained linewidths in very good agreement with the experimental results. We have also found that this scaling introduces a very small (2%) change in the total potential around the van der Waals minimum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467597
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