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  • 1
    Electronic Resource
    Electronic Resource
    Determination of Density of Small Fragments (1954)
    s.l. : American Chemical Society
    Analytical chemistry 26 (1954), S. 1515-1517 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac60093a035
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  • 2
    Electronic Resource
    Electronic Resource
    Benchmark calculations of thermal reaction rates. II. Direct calculation of the flux autocorrelation function for a canonical ensemble (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2045-2056 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermal rate coefficient for the benchmark reaction H+H2→H2+H with zero total angular momentum is calculated by an L2 basis-set evaluation of the flux autocorrelation function. This involves the direct evaluation of the thermally averaged flux operator without calculating any state-to-state reaction probabilities. The results are internally converged to 0.1% and agree with the totally independent results of the previous paper to within 0.03%. This confirms that the correlation-function approach is stable enough to converge practical calculations to three or more significant figures, which is adequate for all purposes, and that the calculations of this and the previous paper may be used to test the convergence and accuracy of other methods for calculating canonical-ensemble reaction rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459926
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  • 3
    Electronic Resource
    Electronic Resource
    Calculation of thermal rate coefficients from the quantum flux autocorrelation function: Converged results and variational quantum transition state theory for O+HD↔OD+H and O+HD↔OH+D (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5097-5112 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermal rate coefficients for the title reactions with zero total angular momentum are calculated by an L 2 basis-set evaluation of the flux autocorrelation function. We use three dividing surfaces, each one separating one arrangement from the other two. The rate coefficients for O+HD↔OD+H or OH+D are converged to within 1.2% over the temperature range 300–1000 K and to within 2.4% at 200 K. The rate coefficients for the reactions H+OD↔D+OH are converged to within 22% at 1000 K and upper bounds to these rate coefficients are given for the temperature range 200–800 K. Flux autocorrelation functions and rate coefficients are calculated for different positions of the dividing surface to show that the computed rate coefficient is stable with respect to varying this position. Rate coefficients are also calculated by a variational version of quantum mechanical transition state theory and the results are compared to the accurate rate coefficients obtained from flux autocorrelation function theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461677
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  • 4
    Electronic Resource
    Electronic Resource
    The calculation of highly excited bound-state energy levels for a triatomic molecule by using three-arrangement basis sets and contracted basis functions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6615-6621 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rovibrational energy levels of the nonrotating H+3 molecular ion have been calculated using a basis set defined in three-arrangement Jacobi coordinates. Energy levels corresponding to the A'1 symmetry are reported up to 22 600 cm−1 above the potential energy minimum and are converged to within 1.8 cm−1, energy levels in the A2 symmetry are reported up to 28 800 cm−1 and are converged to within 0.7 cm−1, and energy levels in the E' symmetry are reported up to 24 300 cm−1 and are converged to within 1.8 cm−1. The maximum deviation of the reported results from the results of Carter and Meyer [J. Chem. Phys. 93, 8902 (1990)] is about 2 cm−1, and most of the results agree to within 1 cm−1. An advantage to our basis set is that it can represent the full D3h symmetry of this system, and thus the energy levels are assigned to the correct symmetry group unambiguously. In order to improve computational efficiency, contracted basis functions were formed using a successive diagonalization-truncation procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461531
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  • 5
    Electronic Resource
    Electronic Resource
    The accuracy of second order perturbation theory for multiply excited vibrational energy levels and partition functions for a symmetric top molecular ion (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4948-4958 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational energy levels and partition functions of the nonrotating H3+ molecular ion have been calculated by using second order perturbation theory, including constant, linear, and quadratic terms in the vibrational quantum numbers. Energy levels have been assigned to A'1, A'2, and E' symmetry species up to 29 244 cm−1, and perturbation theory energy levels have been compared with the results of accurate quantum calculations. The root-mean-square error in 141 energy levels is 4.0 cm−1, as compared to 11.7 cm−1 in the harmonic approximation. Furthermore, perturbation-theory partition functions have errors of 7.4% or less over the factor-of-20 temperature range from 200 to 4000 K. The effect of the constant term in perturbation theory is also discussed; it improves the vibrational partition functions by ∼4% at 200 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464950
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  • 6
    Electronic Resource
    Electronic Resource
    The Extractability of Vitamin G (B2) from Yeast by Various Acetone—Water and Methyl Alcohol—Water Mixtures (1934)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 56 (1934), S. 452-454 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja01317a052
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  • 7
    Electronic Resource
    Electronic Resource
    Ab Initio Study of the Ring-Opening Reactions of Pyran, Nitrochromene, and Spiropyran (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 9730-9738 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100024a014
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  • 8
    Electronic Resource
    Electronic Resource
    A study of water clusters using the effective fragment potential and Monte Carlo simulated annealing (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 2063-2073 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Simulated annealing methods have been used with the effective fragment potential to locate the lowest energy structures for the water clusters (H2O)n with n=6, 8, 10, 12, 14, 16, 18, and 20. The most successful method uses a local minimization on each Monte Carlo step. The effective fragment potential method yielded interaction energies in excellent agreement with those calculated at the ab initio Hartree–Fock level and was quite successful at predicting the same energy ordering as the higher-level perturbation theory and coupled cluster methods. Analysis of the molecular interaction energies in terms of its electrostatic, polarization, and exchange-repulsion/charge-transfer components reveals that the electrostatic contribution is the dominant term in determining the energy ordering of the minima on the (H2O)n potential energy surfaces, but that differences in the polarization and repulsion components can be important in some cases. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480775
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  • 9
    Electronic Resource
    Electronic Resource
    An effective fragment method for modeling solvent effects in quantum mechanical calculations (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1968-1986 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An effective fragment model is developed to treat solvent effects on chemical properties and reactions. The solvent, which might consist of discrete water molecules, protein, or other material, is treated explicitly using a model potential that incorporates electrostatics, polarization, and exchange repulsion effects. The solute, which one can most generally envision as including some number of solvent molecules as well, is treated in a fully ab initio manner, using an appropriate level of electronic structure theory. In addition to the fragment model itself, formulae are presented that permit the determination of analytic energy gradients and, therefore, numerically determined energy second derivatives (hessians) for the complete system. Initial tests of the model for the water dimer and water-formamide are in good agreement with fully ab initio calculations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472045
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  • 10
    Electronic Resource
    Electronic Resource
    Density functional theory studies of meso-alkynyl porphyrins (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2504-2510 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Geometry optimizations and electronic structure calculations are reported for porphyrins with meso-acetylene substituents using density functional theory (DFT). The addition of the acetylene group alters the nearest C–C bond length in the porphyrin ring by 0.01 to 0.02 Å, but the molecule retains its D2h symmetry. The calculated electronic structures clearly show that the acetylene group contributes to the π-electron conjugation along the porphyrin ring for the HOMO and LUMO, and reduces significantly the HOMO-LUMO gap, being consistent with experimental results [H. L. Anderson, Tetrahedron Lett. 33, 101 (1992)]. The core ionization potential (IP) of the central nitrogen calculated using the so-called local density approximation effective core (LDAEC) method, is increased by 0.24 eV, indicating a more positive electrostatic potential than in PH2. LDA-ΔSCF results for the first three valence IPs indicate changes of 0.1 to 0.2 eV relative to those of the free-base porphin, with the gap between the first and second IPs being over twice as large in the acetylated molecule. The protective trimethylsilyl (TMS) group further reduces the HOMO-LUMO gap, but by a small amount. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475633
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