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  • 1
    Electronic Resource
    Electronic Resource
    Proton–donor properties of water and ammonia in van der Waals complexes with rare-gas atoms. Kr–H2O and Kr–NH3 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8181-8187 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The perturbation theory of intermolecular forces in conjunction with the supermolecular Møller–Plesset perturbation theory is applied to the analysis of the potential-energy surfaces of Kr–H2O and Kr–NH3 complexes. The valleylike minimum region on the potential-energy surface of Kr–H2O ranges from the coplanar geometry with the C2 axis of H2O nearly perpendicular to the O–Kr axis (T structure) to the H-bond structure in which Kr faces the H atom of H2O. Compared to the previously studied Ar–H2O [J. Chem. Phys. 94, 2807 (1991)] the minimum has more of the H-bond character. The minimum for Kr–NH3 corresponds to the T structure only, in accordance to the result for Ar–NH3 [J. Chem. Phys. 91, 7809 (1989)]. The minima in Kr–H2O and Kr–NH3 are roughly 27% and 19%, respectively, deeper than for the analogous Ar complexes. To examine the proton–donor abilities of O–H and N–H bonds the ratios of the deformation energy to dispersion energy are considered. They reflect fundamental differences between the two bonds and explain why NH3 is not capable of forming the H-bond structures to rare-gas atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463440
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio study of intermolecular potential for ArHCl (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6677-6685 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential energy surface of ArHCl. Two minima have been found, a primary for collinear Ar–HCl and a secondary for collinear Ar–ClH. The depths of these minima are about 12% below the empirical estimates, due to basis set unsaturation of the dispersion contribution. The Ar–HCl structure is favored by the induction and dispersion terms whereas Ar–ClH by the exchange–repulsion term. The total ab initio potential, as well as its components, are compared with related terms of recent Hutson's H6(3) potential [J. Chem. Phys. 89, 4550 (1988)] and the anisotropy of interaction is analyzed. It is concluded that the one-center multipole expansions of induction and dispersion contributions do not reproduce the correct anisotropy of induction and dispersion terms. Ab initio estimates of three-body effects in the Ar2HCl complex are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460244
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational frequencies and intensities of H-bonded and Li-bonded complexes. H3N⋅⋅HCl and H3N⋅⋅LiCl (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3131-3138 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometries, energetics, and vibrational spectra are calculated for the two complexes at the SCF and correlated MP2 levels using the 6-31G** basis set, augmented by a second set of d functions on Cl. While correlation represents an important factor in the binding of H3 N⋅⋅HCl, it contributes little to the stronger Li bond. Unlike the HCl stretch νs which decreases substantially in frequency and is greatly intensified in H3 N⋅⋅HCl, the frequency of the LiCl stretch undergoes an increase and little change is noted in its intensity, conforming to prior spectral measurements. The intensities of the intramolecular stretching modes of NH3 are greatly strengthened by formation of a H bond and even more so for a Li bond. These intensity patterns are analyzed via atomic polar tensors which reveal that formation of a H bond dramatically lessens the ability of the electron density to shift along with the proton. A stretch of H–Cl hence leads to a large increase in molecular dipole moment. This "freezing'' of the electron cloud is much smaller in the Li bond and its effect on the νs intensity is counteracted by a much reduced Li atomic charge in the complex. Another distinction between the H and Li bonds relates to the destination of charge transferred from the NH3 subunit which accumulates on Cl in the former case but on Li in the latter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454970
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  • 4
    Electronic Resource
    Electronic Resource
    Ab initio study of the intermolecular potential of Ar–H2O (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2807-2816 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential-energy surface of Ar–H2O. The surface is very isotropic with the lowest barrier for rotation of ∼35 cm−1 above the absolute minimum. The lower bound for De is found to be 108 cm−1 and the complex reveals a very floppy structure, with Ar moving freely from the H-bridged structure to the coplanar and almost perpendicular arrangement of the C2 –water axis and the Ar–O axis, "T-shaped'' structure. This motion is almost isoenergetic (energy change of less than 2 cm−1 ). The H-bridged structure is favored by the attractive induction and dispersion anisotropies; the T-shaped structure is favored by repulsive exchange anisotropy. The nonadditive effect in the Ar2–H2O cluster was also calculated. Implications of our results on the present models of hydrophobic interactions are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459857
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  • 5
    Electronic Resource
    Electronic Resource
    Calculations of nonadditive effects by means of supermolecular Møller–Plesset perturbation theory approach: Ar3 and Ar4 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2481-2487 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonadditive, multibody effects arising in the supermolecular Møller–Plesset perturbation theory (MPPT) (IMPPT) calculations are classified and interpreted in terms of the exchange, induction, deformation, and dispersion contributions, as defined by the perturbation theory of intermolecular forces. As an example the many-body effects in the equilateral Ar trimer and tetrahedral Ar tetramer, calculated through the MP4 level of theory with extended basis [7s4p2d], are reported and discussed. It is stressed that the "Heitler–London-exchange plus dispersion'' model for nonadditive effects is too attractive mainly because of the neglect of the second-order exchange contribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457991
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  • 6
    Electronic Resource
    Electronic Resource
    Intermolecular potential of H2O⋅⋅⋅H2 in the van der Waals region. An ab initio study (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6039-6047 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The fourth-order Møller–Plesset perturbation theory is used to evaluate the intermolecular potential of the H2O⋅⋅⋅H2 system with special emphasis on the van der Waals well region. When interacting with H2O, the H2 molecule can act either as a proton donor or as a proton acceptor. In the minimum energy configuration (−197 cm−1), H2 approaches the O atom collinearly with the C2 axis of H2O. In the secondary attractive region (−184 cm−1), H2 forms a T-shaped structure with the O–H bond of H2O (the H2 axis is perpendicular to the H2O plane). Other attractive areas of the potential are also examined. The origins of anisotropy of the interaction potential are studied by dissecting the interaction energy into its components—electrostatic, exchange repulsion, dispersion, deformation, etc. The potential energy surface is highly anisotropic, due largely to electrostatic interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462645
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  • 7
    Electronic Resource
    Electronic Resource
    Analysis of the intermolecular potential of Ar–CH4: An ab initio study (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 463-469 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The perturbation theory of intermolecular forces in conjunction with the supermolecular Møller–Plesset treatment is applied in the analysis of the potential energy surface of Ar–CH4. The anisotropy of the Ar–CH4 potential energy surface is chiefly due to exchange repulsion. In the equilibrium structure, Ar approaches the face of CH4 tetrahedron thus avoiding contacts with C–H bonds. The equilibrium Ar–C separation was found equal to 7.5 a0 and the De energy to 113 cm−1. We estimate that our De may be too small by up to 25% with respect to the accurate value. The properties of Ar–CH4 are also compared with other Ar-molecule systems, such as Ar–NH3, Ar–H2O, and Ar–HCl. We find that the equilibrium structures of weak proton donors bound to Ar (CH4, NH3) are determined by the exchange repulsion, while those of efficient proton donors, such as HCl (and to a lesser extent H2O), result from the strong polarization of Ar in the field of a molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462482
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of the potential energy surface of Ar–NH3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7809-7817 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential energy surface of Ar–NH3. Anisotropy of the self-consistent field (SCF) potential is determined by the first-order exchange repulsion. Second-order dispersion energy, the dominating attractive contribution, is anisotropic in the reciprocal sense to the first-order exchange, i.e., minima in one nearly coincide with maxima in the other. The estimated second-order correlation correction to the exchange effect is nearly as large as a half ΔESCF in the minimum and has a "smoothing'' effect on the anisotropy of ε(20)disp. The model which combines ΔESCF with dispersion energy (SCF+D) is not accurate enough to quantitatively describe both radial and angular dependence of interaction energy. Comparison is also made between Ar–NH3 and Ar–PH3, as well as with the Ar dimer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457249
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  • 9
    Electronic Resource
    Electronic Resource
    Ab initio study of intermolecular potential of H2O trimer (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2873-2883 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonadditive contribution to the interaction energy in water trimer is analyzed in terms of Heitler–London exchange, SCF deformation, induction and dispersion nonadditivities. Nonadditivity originates mainly from the SCF deformation effect which is due to electric polarization. However, polarization does not serve as a universal mechanism for nonadditivity in water. In the double-donor configuration, for example, the Heitler–London exchange contribution is the most important and polarization yields the wrong sign. Correlation effects do not contribute significantly to the nonadditivity. A detailed analysis of the pair potential is also provided. The present two-body potential and its components are compared to the existing ab initio potentials (MCY) as well as to empirical ones (RWK2,TIP,SPC). The ways to improve these potentials are suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459809
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  • 10
    Electronic Resource
    Electronic Resource
    Intermolecular potential of the methane dimer and trimer (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4243-4253 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Heitler–London (HL) exchange energy is responsible for the anisotropy of the pair potential in methane. The equilibrium dimer structure is that which minimizes steric repulsion between hydrogens belonging to opposite subsystems. Dispersion energy, which represents a dominating attractive contribution, displays an orientation dependence which is the mirror image of that for HL exchange. The three-body correction to the pair potential is a superposition of HL and second-order exchange nonadditivities combined with the Axilrod–Teller dispersion nonadditivity. A great deal of cancellation between these terms results in near additivity of methane interactions in the long and intermediate regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458757
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