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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio study of the hydroxide ion–water clusters: An accurate determination of the thermodynamic properties for the processes nH2O+OH−→HO−(H2O)n (n=1–4) (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 4045-4052 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Clusters of hydroxide ion, HO−(H2O)n=1–4, have been studied by high level ab initio calculations in order to better understand the first coordination shell of OH− ions. Geometry optimizations were performed at Hartree–Fock, density functional theory and second order Møller–Plesset perturbation theory levels using the 6-31+G(d,p) basis set. Single point energy calculations were carried out on the optimized geometries using the more extended 6-311+G(2df,2p) basis set and a higher level of electron correlation, namely fourth-order Møller–Plesset perturbation theory. For the n=1–3 clusters, only structures with the hydroxide ion hydrogen bonded to all waters molecules were considered. For the n=4 cluster, three minima were found; the most stable species has all four waters directly bound to the hydroxide ion, while the other two clusters have only three waters in the first coordination shell. In addition, the transition state connecting the cluster containing four waters in the first coordination shell to the species having three waters in the coordination shell was characterized. The barrier for this rearrangement is very low (1.82 kcal/mol), and we predict this process to occur on the picosecond time scale. The thermodynamic properties (enthalpy, entropy and Gibbs free energy) for the formation of the clusters have been calculated for all the species (including the fully deuterated clusters). Comparison of our calculations with experimental data reveals good agreement in the free energy. Nevertheless, our ab initio results suggest that for the n〉1 clusters, both −ΔH0 and −ΔS0 are larger than those reported from experiment and new experiments may be necessary to obtain accurate experimental values. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480954
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio MP2 study of the HF ... ClF complex using various extended basis sets and bond functions (1996)
    Springer
    Theoretical chemistry accounts 93 (1996), S. 333-342 
    Details
    ISSN: 1432-2234
    Keywords: van der Waals complex ; Transition states ; Extended basis sets ; Bond functions ; Electronic correlation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The stationary points on the intermolecular potential energy surface (PES) for the HF ... ClF complex have been investigated at the second-order Møller-Plesset perturbation theory (MP2) level using various extended bais sets, including diffuse functions, and also bond functions. The last ones were placed at different intermolecular positions, for distinct stationary points. The basis set superposition errors (BSSE) were accounted for using the counterpoise method. Besides the anti-H-bonded and H-bonded minimum energy structures, four transition state structures were also located on the PES. It was shown that higher polarization functions are required for the description of the anti H-bonded isomer and diffuse functions had to be included for the H-bonded isomer. The bond functions are able to replace thef (Cl, F) andd(H) polarization functions at a lower computational cost. However, for the H-bonded isomer intramolecular electron correlation also plays an important role. So we have to use diffuse nucleus centered polarization functions for an adequate description of intermolecular and intramolecular correlation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01129214
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio conformational analysis of cyclooctane molecule (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 524-534 
    Details
    ISSN: 0192-8651
    Keywords: ab initio conformational analysis ; cyclooctane molecule ; potential energy surface ; Hartree-Fock theory ; Møller-Plesset theory ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The potential energy surface (PES) for the cyclooctane molecule was comprehensively investigated at the Hartree-Fock (HF) level of theory employing the 3-21G, 6-31G, and 6-31G* basis sets. Six distinct true minimum energy structures (named B, BB, BC, CROWN, TBC, and TCC1), characterized through harmonic frequency analysis, were located on the multidimensional PES. Two transition state structures were also located on the PES for the cyclooctane molecule. Electron correlation effects were accounted for using the Møller-Plesset second-order perturbation theory (MP2) approach. The predicted global minimum energy structure on the ab initio PES for the cyclooctane molecule is the BC conformer. A gas phase electron diffraction study at 300 K suggested a conformational mixture while an NMR study in solution at 161.5 K predicted the BC conformer as the predominant form. The equilibrium constants reported in the present study, which were evaluated from the ab initio calculated total Gibbs free energy change values, were in good agreement with both experimental investigations. The ab initio results showed that the low temperature condition significantly favored the BC conformer while above room temperature both BC and CROWN structures can coexist.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 524-534, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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