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101.
DAVID J. WALES 《Molecular physics》2013,111(20):3285-3305
A theoretical framework is developed for the calculation of rate constants by sampling connected pathways composed of local minima and transition states that link them together. The theory is applicable to two-state or effective two-state systems and is applied to permutational or morphological isomerization in a two-dimensional cluster of seven Lennard-Jones atoms, water clusters containing eight and nine molecules, and a cluster of 38 Lennard-Jones atoms, which exhibits a double funnel energy landscape. 相似文献
102.
According to both UB3LYP/6-311G* and UMP2/6-311G* calculations, the lowest energy conformer of the S+ 8 radical cation possesses Cs symmetry. However, there are three other structures with low relative energies that do not exceed 6.5 kcal mol?1. These conformers, which are found to be very prone to pseudorotation, are predicted to interconvert readily. The fluxional nature of S+ 8 is expected to facilitate its reactions with organic species where a specific conformation is demanded by steric constraints, which may explain its high reactivity towards PAHs with crowded hydrogen atoms. 相似文献
103.
DAVID P. DOBSON JOHN P. BRODHOLT LIDUNKA VOČADLO WILSON A. CRICHTON 《Molecular physics》2013,111(10):773-777
Experiments have been performed at 5 GPa on liquid Fe-FeS in order to determine Fe and S self-diffusivity as a function of temperature. The viscosity of the sample was then obtained using the Stokes-Einstein relation. The results are in excellent agreement with previous experiments where the viscosity of a material of the same composition under similar conditions was measured directly. These results support high, near-metallic, values of diffusivity and low viscosity in liquid Fe-S up to a few hundred K above the eutectic temperature, in contrast with some previous studies. Moreover, these results fully confirm the validity of the Stokes-Einstein relation between viscosity and diffusion coefficients for Fe0.61S0.39. 相似文献
104.
105.
Numerical Solution of Volterra Integral Equations with Continuous or Discontinuous Terms 总被引:1,自引:0,他引:1
Convergence criteria are given for the numerical solution ofVolterra integral equations with and without discontinuous terms.Several numerical methods are compared. 相似文献
106.
107.
Structure indices for multidimensional systems 总被引:1,自引:0,他引:1
WOOD JEFFREY; ROGERS ERIC; ROCHA PAULA; OWENS DAVID H. 《IMA Journal of Mathematical Control and Information》2000,17(3):227-256
The structure indices of a one-dimensional system are an importantset of invariants. In this paper we examine a generalizationof this concept to multidimensional linear systems, which correspondsto the algebraic concept of a Hilbert series. We use the standardtheory of the Hilbert series to explain some of the previousID system-theoretic results. We discuss the computation of nDstructure indices from an initial condition set, and the invariantswhich can be derived from these indices. 相似文献
108.
Molecular mobility is studied in poly(butyl methacrylate) isomers with molecular dynamics simulations in order to understand the role of the side chain steric hindrance on the β and δ relaxation mechanisms. The simulations suggest that in the temperature range studied the δ process is weakly influenced by the α process. Conversely, the β process seems to be significantly changed as compared with the low frequency regime. The results exposed also show evidence that the intramolecular cooperativity is higher in PnBMA than in PtBMA, which, could be related to the distance to the α-β crossover. 相似文献
109.
FENG LONG GU YURIKO AOKI AKIRA IMAMURA DAVID M. BISHOP BERNARD KIRTMAN 《Molecular physics》2013,111(10):1487-1494
A novel finite-field approach for calculating electric (hyper)polarizabilities based on the elongation method is developed. The method was tested at the semi-empirical PM3 level by using three model systems: the hydrogen chain, the water chain and polyacetylene. The results satisfactorily reproduce the ‘exact’ MOPAC values. The most important advantage of this approach is the large saving of computer time since the dimension of the SCF equation remains the same regardless of the number of atoms in the system. Thus, it is a very useful tool to treat large systems. The method can also be applied to building up a chain containing an arbitrary sequence of monomers. 相似文献
110.
DAVID B. DAVIES DENNIS A. VESELKOV VENIAMIN V. KODINTSEV MAXIM P. EVSTIGNEEV ALEXEI N. VESELKOV 《Molecular physics》2013,111(23):1961-1971
Hetero-association of the anthracycline drug, daunomycin (DAU), with typical mutagens, the acridine dyes proflavine (PF) and acridine orange (AO), has been studied by 500 MHz 1H NMR spectroscopy as a function of concentration and temperature in 0.1 mol dm?3 phosphate buffered aqueous solutions at pD = 7.1. The results have been analysed in terms of a statistical-thermodynamical model of hetero-association of aromatic molecules, described previously [Davies, D. B., Veselkov, D. A., and Veselkov, A. N., 1999, Molec. Phys., 97, 439], but generalized in this work, so that there is no limitation on the magnitudes of the self-association constants of the interacting molecules. Expressions suitable for the analysis of NMR parameters of both components in the mixed solution have been developed enabling both the structural and thermodynamic properties of hetero-association to be determined. The magnitude of the equilibrium constant for hetero-association of PF + DAU is found to be substantially higher than the self-association constants of these molecules, whereas that for hetero-association of AO + DAU is intermediate between the equilibrium constants of self-association of AO and DAU. Intermolecular cross-peaks observed in 2D-ROESY spectra of PF + DAU mixed solutions are consistent with formation of a hetero-association complex in which an intermolecular hydrogen bond can form between either of the 3,6-diamino groups of the PF chromophore and the 9-MeCO group of DAU, which is in contrast to AO + DAU hetero-association, where such hydrogen bonds are unable to form. Quantitative structural and thermodynamical analysis of PF + DAU complexation is consistent with an intermolecular hydrogen bond contributing to the stability of the hetero-complex in aqueous solution. The NMR results show that hydrophobic interactions play a substantial role in the stabilization of the AO-DAU complex, characterized by a relatively small entropy change on complexation, compared to the PF-DAU hetero-complex, which is mainly stabilized by hydrogen bond and dispersive van der Waals interactions. 相似文献