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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    A theoretical study of the water dimer interaction (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3662-3673 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed a study of the water dimer interaction using larger basis sets and higher levels of theory than have been previously applied to this system. For the minimum geometry we have used spdf basis sets containing up to 212 orbitals. Our most accurate SCF interaction energy for the minimum is −3.73±0.05 kcal/mol. We have shown that this energy can be reproduced to within 0.1 kcal/mol using much smaller basis sets containing proper (diffuse) exponents. Accounting for the basis set superposition error is shown to be essential. We computed the dispersion energy with neglect of the intramolecular correlation using basis sets of various sizes. The best value obtained in a large spdf basis set with exponents which optimize this quantity is −1.93 kcal/mol and it is expected to be accurate to 0.1 kcal/mol or better. Using some of these basis sets we have performed supermolecular many-body perturbation theory (MBPT) and coupled-cluster (CC) calculations including triple excitations. We have shown that if the correlated supermolecular interaction energies are not corrected for the basis set superposition error, the correlated part of the interaction energy varies widely with the basis set. In contrast, the corrected values converge smoothly. On the basis of the dispersion energy and the MBPT/CC results we predict the correlated part of the interaction energy to be −1.0±0.3 kcal/mol, which leads to the total interaction energy of −4.7±0.35 kcal/mol. Thus, our work favors the lower limit of the experimentally predicted interaction energy of −5.4±0.7 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454886
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  • 3
    Electronic Resource
    Electronic Resource
    The role of symmetry in collisions of N2 with N+2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6500-6507 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical trajectory methods have been used to explore the excitation of vibrations in gas-phase collisions of the nitrogen molecular ion with its parent molecule. The near symmetry of the reactants is shown to result in a high probability that the two molecules are excited by an equal amount of energy. This provides a possible explanation of the molecular beam measurements that show that the total number of vibrational energy quanta excited in the collision is, with a high probability, even.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460278
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  • 4
    Electronic Resource
    Electronic Resource
    Atomic and molecular correlation energies with explicitly correlated Gaussian geminals. V. Cartesian Gaussian geminals and the neon atom (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3964-3974 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Correlation energy through third order and various coupled-pair correlation energies have been calculated for the neon atom using a basis set of explicitly correlated Gaussian geminals. Improved versions of functionals introduced in earlier papers of this series have been used. Our results are in very good agreement with accurate results of Lindgren and Salomonson and Jankowski et al. obtained with techniques specific for atoms. Our values are estimated to be accurate to about 1 mhartree. The results of this paper show that the method of Gaussian geminals is very competitive for systems with p electrons and should be able to achieve "chemical accuracy'' for small molecules containing first and second row atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450918
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  • 5
    Electronic Resource
    Electronic Resource
    Intraatomic correlation effects for the He–He dispersion and exchange–dispersion energies using explicitly correlated Gaussian geminals (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5652-5659 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The coupling of the intermolecular interaction with the intramolecular correlation effects is considered using the coupled cluster (CC) formalism. The CC equations for the dispersion energy are presented and their relation to the double perturbation theory is analyzed. An approximate scheme based on partial decoupling of the CC equations is applied for the He–He interaction. Numerical results are obtained using explicitly correlated Gaussian geminal basis set. They confirm the importance of the intraatomic (apparent) correlation effects and agree very well with the experimentally derived potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452542
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  • 6
    Electronic Resource
    Electronic Resource
    Complete ab initio three-body nonadditive potential in Monte Carlo simulations of vapor–liquid equilibria and pure phases of argon (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9518-9531 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Complete ab initio three-body nonadditivity, including the short-range contributions, has been used for the first time in Monte Carlo simulations of liquid, gas, and liquid–vapor equilibrium of argon. Very good overall agreement with experiment has been achieved for phase equilibrium parameters and pV data of pure phases. The importance of various three-body interaction components has been assessed and their relationship to the liquid structure has been investigated. Although the short-range contributions to the nonadditivity are quite large, cancellations occurring between these and other components at the interatomic distances typical for the liquid make the total three-body nonadditive effect very similar to that given by a simple triple-dipole potential. Performance of the three-term virial equation of state is assessed based on the results of simulations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1370084
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  • 7
    Electronic Resource
    Electronic Resource
    Intermolecular potential energy surfaces and spectra of Ne–HCN complex from ab initio calculations (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 764-779 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio calculations of five two-dimensional intermolecular potential energy surfaces of the Ne–HCN dimer have been performed using the symmetry-adapted perturbation theory and the supermolecular method at different levels of electron correlation. A basis set of spdf-symmetry orbitals (including midbond functions) was used. HCN was assumed linear with interatomic distances fixed at their vibrationally averaged 〈r−2〉−1/2 values. Fits to all calculated potential energy surfaces were obtained in the form of angular expansions incorporating the ab initio asymptotic coefficients. It has been found that high-order correlation effects are very important for Ne–HCN and contribute about 20% to the well depth. All of the five surfaces feature a global minimum at the linear Ne–HCN geometry and a narrow and relatively flat valley surrounding HCN. Rovibrational calculations on the surfaces yielded rotational spectra and a rotational constant whose relative differences from their experimental counterparts range from 2% to 12% depending on the method used to obtain the surface. This large sensitivity of spectral quantities to relatively modest differences between the potentials is related to the unusual shape of the potential well. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331101
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  • 8
    Electronic Resource
    Electronic Resource
    Second-order correlation energy for H2O using explicitly correlated Gaussian geminals (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 888-897 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The second-order pair energies are calculated for the H2O molecule employing explicitly correlated Gaussian-type geminals. The selection of the basis functions is guided by the completeness criteria for Gaussian geminal bases of C2v symmetry and by the recently developed technique [J. Chem. Phys. 100, 1366 (1994)] of crude optimization of nonlinear geminal parameters. Several simplifications have been made in the matrix elements evaluations that substantially reduce the optimization time without sacrificing numerical accuracy. The present results provide the new best upper bound to the second-order correlation energy for the water molecule. These results are compared with those obtained by Kutzelnigg and co-workers using the basis set containing terms linear in the interelectronic distance. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469155
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    New effective strategy of generating Gaussian-type geminal basis sets for correlation energy calculations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1366-1374 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gaussian-type geminal basis sets for correlation energy calculations are usually obtained by optimization of the second-order energy functional. In the present work we propose a new strategy of generating the initial sets of geminals for these optimizations. Taking advantage of the information about the analytical structure of the second-order pair functions, this strategy produces reasonable starting values of the nonlinear geminal parameters, which lead to accurate second-order energies after only a short, crude reoptimization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466614
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