摘要:

The molecular-dynamics method has been used to study carbon dioxide physisorbed on the basal plane of graphite at temperatures between 100 and 130K at monolayer and submonolayer coverages. Additionally, energy-minimization calculations have been used to explore the relative stability of a number of solid structures of the adsorbate. Three models of carbon dioxide, which have been successful in describing the properties of the bulk phase, where tested in these simulations of the adsorbate. The results at submonolayer coverage suggest that the adsorbate forms a two-sublattice incommensurate herringbone structure. These solid patches have approximately the correct melting point. At monolayer coverage the existence of a four-sublattice pinwheel structure was only observed for a model with an artificially enhanced quadrupole moment. Further refinement of the potential model will require additional calorimetric or diffraction experiments.

ISSN:0026-8976    

DOI:10.1080/00268979000100931

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A new two-step evaporation technique has been developed by which the particles in a silver island film grow with parallel alignment and low symmetry. In contrast with rotationally symmetric particles prepared in the usual way of island evaporation, films of such particles shown second-harmonic generation (SHG) in transmission and reflection when irradiated normally to the substrate plane. Although silver atoms arrange in a centrosymmetric crystal lattice, such specially prepared island films behave like a film of a non-centrosymmetric material. Owing to localized plasma oscillation resonances in the particles, the SH is strongly enhanced. The measured SH efficiency exceeds the SH from an α-quartz sheet of equal thickness by a factor of order 104.

ISSN:0026-8976    

DOI:10.1080/00268979000100941

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We show that the computer simulation ‘colour-conductivity’ experiment that is used in non-equilibrium molecular dynamics to determine the kinetic partdof the mutual-diffusion coefficient of a binary mixture of non-electrolytes may be interpreted as a sedimentation experiment. Correspondingly, the expression that relates the colour conductivity todis a special case of the Svedberg relation.

ISSN:0026-8976    

DOI:10.1080/00268979000100951

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Density profiles for inhomogeneous dense Lennard-Jones fluids in narrow planar slits are calculated using various integral-equation closures for the anisotropic pair distribution functions. Very good agreement with simulation studies is obtained for the Zerah-Hansen (ZH) closure and a variant of the modified hypernetted chain (MHNC) closure suggested here while the Percus-Yevick (PY), the soft-core mean spherical approximation (SMSA) and, in particular, the hypernetted chain (HNC) closures give inferior results. Various properties of the fluid as functions of the slit width are calculated in the ZH approximation, using closure parameters optimized for the bulk phase. The mean particle number per unit area virtually coincides with the values from grand canonical ensemble simulations. The net pressure between the walls, which is more difficult to calculate accurately, agrees well with the simulation result. The agreement can probably be further improved by fully optimizing the ZH closure for the inhomogeneous system.

ISSN:0026-8976    

DOI:10.1080/00268979000100961

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Classical-trajectory calculations are reported using two recent potentialenergy surfaces—the theoretical surface of Bowerset al.and the multiproperty fit of Gianturcoet al.Comparisons with measurements of diffusion, viscosity, thermal conductivity, rotational relaxation, depolarized Rayleigh light scattering and magnetic-field effects on diffusion, viscosity and thermal conductivity show generally better agreement than obtained using the earlier (HFD1) surface of Fuchset al., but some differences remain. Overall the surface of Bowerset al.is more reliable but it tends to be insufficiently anisotropic. Results using the infinite-order-sudden approximation are compared with the classical-trajectory results where possible. While errors in the traditional transport properties are small (<2%), errors in properties directly related to the anisotropy are much larger and can exceed 40% for the viscomagnetic-effect relaxation cross-section.

ISSN:0026-8976    

DOI:10.1080/00268979000100971

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The classical limits of the quantal generalized cross-sections for transport and line-broadening phenomena have been derived using classicalS-matrix theory and various semiclassical expressions for the Wigner coefficients. For transport processes, these limits are found to be in agreement with those obtained from a direct classical approach. Explicit expressions are given for the Senftleben-Beenakker effect thermal-conductivity cross-sections.

ISSN:0026-8976    

DOI:10.1080/00268979000100981

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The chemical picture for the transport of matter across a liquid-liquid interface assumes that the overall process can be adequately described by a single rate constant. The present work is aimed at systematic examination of this principle for particles moving on a model potential surface of a particular shape, which contains either a barrier or a well and which obeys a Smoluchowski equation. A semi-analytic solution is found, and the result is compared with both the mean-passage-time result obtained in the present paper and with other available theories of diffusive processes. These theories, which are practically equivalent for high potential barriers, prove to differ significantly when the barrier height is less than 3kBT. Considering the case of a potential well leads to the conclusion that the transient regime, during which the time evolution of the transfer is not accurately described by the leading exponential of the eigenfunction expansion, is much longer than for a potential barrier. While the common theories of diffusive processes are not applicable to a potential well, the mean-passage-time result still gives the correct time scale for the phenomenon.

ISSN:0026-8976    

DOI:10.1080/00268979000100991

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

For fluids of hard ellipsoids of revolution the pair distribution function can be expressed as an expansion in products of spherical harmonics. In this paper molecular-dynamics results are given for eight coefficients in this expansion and detailed comparisons are made with the hypernetted-chain (HNC) and Percus-Yevick (PY) approximations. Ellipsoids with length-to-breadth ratios of ⅓, 2, 3 and 5 are considered, and in some cases results are reported for different densities. It is shown that both the HNC and PY theories are in reasonable agreement with molecular-dynamics results for prolate particles. The accuracy of the theories improves with decreasing density as expected, but does not depend strongly upon the length-to-breadth ratio for the prolate systems considered. For oblate ellipsoids the HNC theory remains in very good agreement with the molecular-dynamics results but the PY approximation is less accurate, tending to be rather poor for some coefficients.

ISSN:0026-8976    

DOI:10.1080/00268979000101001

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Quantum-mechanical considerations indicate that a reasonable classical model for a diatomic system is one in which bond lengths are constant. Two types of such models may be distinguished: rigid models in which the constant length is imposed from the outset as a geometric constraint and flexible models in which the bond is represented by a stiff spring whose force constant becomes infinite. It has been shown by Honnellet al.that the pressure equations derived on the basis of the two models are equivalent. Here we show that this is also the case for the time-averaged bond forcesfcbandfncb, wherefcbis the constraint force in the bond of the rigid model or the covalent bond force in the flexible model, whilefncbarises from the intermolecular non-covalent forces projected onto the bond direction. We show that these forces satisfy the relationfcb+fncb= 2kT/b, withbthe bond length, and that the bond-force concept and this relation provide physical insight into the various terms (intermolecular and intramolecular) in the pressure equation. The results of molecular-dynamics calculations for model systems are presented that focus on the bond forces, the relative importance of the intra- and intermolecular contributions to the pressure, and the effect of an attractive portion of the non-covalent site-site potential on these quantities. The implications of these results for the treatment of diatomic liquids by first-order perturbation calculations are discussed.

ISSN:0026-8976    

DOI:10.1080/00268979000101011

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

High-resolution infrared and near-infrared spectra have been observed for more than 80 overtone bands of the HCCF molecule, including two CH stretching overtones in the visible region. Many of these have been analysed, and many more are in the course of analysis and will be reported later. All fundamentals have now been rotationally analysed and the equilibrium rotational constant determined. These data provide a testing ground for anharmonic force-field analyses, and they are discussed briefly in this connection.

ISSN:0026-8976    

DOI:10.1080/00268979000101021

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor