摘要:

In this paper we have presented a general scheme whereby the method of Padé approximants may be applied to the power series expansion of time dependent correlation functions. It has been demonstrated by actual numerical calculations, using the computer simulated results of Berne and Harp [5], that even a few terms in the power series expansion are capable of reproducing the correlation curves to a fairly large extent. It is pointed out that the method can be extended to higher orders without the introduction of fitting parameters, and without violating the time parity requirements of the Liouville equation. In the final analysis the method is a truly microscopic method since it relies on the microscopic hamiltonian, and the underlying principles are very straightforward. The basic requirements are the spectral moments, but we do not need many of these as the Padé approximants are highly convergent.

ISSN:0026-8976    

DOI:10.1080/00268978000102531

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The partial averaging of second rank properties of molecules dissolved in liquid crystals and having internal degrees of freedom is discussed in terms of equilibrium statistical mechanics. It is shown that the dependence of the partial average on orientational order is determined only by the nature of the intermolecular potential and not, it is argued, by the relative rates of internal and external motion. This result applies to any form of internal motion and the implications of the theory are discussed for internal motion between discrete molecular conformations, free internal rotation and vibrational motion. An explanation is proposed for the observed, finite dipolar and quadrupolar couplings of nuclei in tetrahedral molecules. This implies that the phenomenon is not necessarily a consequence of a distortion of these molecules in the anisotropic solvent, but does require a dependence of the orientational order on the vibrational state.

ISSN:0026-8976    

DOI:10.1080/00268978000102541

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Mori's continued fraction method has been applied with closure at the second level to the velocity and angular momentum autocorrelation functions (acf) and with closure at the third level to the orientational acfs <Pl(t)>l=1, 2. The acfs were obtained in molecular dynamics simulations of diatomic liquids modelled by 2-Lennard-Jones centres potentials (1,2).

ISSN:0026-8976    

DOI:10.1080/00268978000102551

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Irradiation of a single crystal of Ph3As+CH3I-produces a paramagnetic species exhibiting hyperfine interaction with75As and methyl protons. By studying the angular dependence of the E.S.R. spectra obtained from X- irradiated crystals of Ph3As+CD3I-and Ph3As+13CH3I-the following tensors have been obtained:ǥ, quadrupolar interaction with75As, magnetic hyperfine coupling with75As and13C. These parameters show that ∼75 per cent of the spin is localized on the methyl carbon and lead to the identification of the novel adduct Ph3As … ĊH3. The directions of the eigenvectors show that theC3axes of Ph3As and ĊH3are probably not colinear. The structure of the adduct is compared to that of phosphoranyl radicals.

ISSN:0026-8976    

DOI:10.1080/00268978000102561

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The decoupling of dipolar proton-proton interactions by a strong second radio frequency field in ENDOR spectroscopy is reported. A theoretical description of the decoupling effect for a system with one electron and two nuclear spins of ½ is given for anisotropicgand hyperfine tensors. The results indicate that the hyperfine tensor of the pumped nucleus influences the decoupling behaviour remarkably. Transition frequencies and intensities predicted by theory are compared with experimental data from Cu(gly)2in α-glycine. Further applications of this spin decoupling technique are discussed. As an example, the assignment of ENDOR proton lines to specific water molecules in Cu2+: (NH4)2Mg(SO4)2·6H2O is presented.

ISSN:0026-8976    

DOI:10.1080/00268978000102571

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

We present a new rigorous upper bound for the Helmholtz free energy of the Restricted Primitive Model of ionic liquids. For this model, the bound is more powerful than a previous bound due to Rasaiah and Stell. It is based on the notion that the free energy of an ionic liquid may always be reduced below that of the perfect gas by the formation of bound pairs of oppositely charged ions. The upper bound may be used to test the free energy predicted by particular approximations. The mean spherical approximation, when tested in this way, turns out to give a serious overestimate of the free energy at low temperatures and densities. We point out the implications of this result for recent discussions, based on that approximation, concerning liquid-vapour equilibrium and the position of the critical point.

ISSN:0026-8976    

DOI:10.1080/00268978000102581

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Monte Carlo simulations are reported for 45 state points of the hard dumbell system covering elongationsl/σfrom 0·2 to 1·0 and densitiesσd3from 0·2 to 0·9 (lis the bond length, σ the atom diameter and thedthe diameter of a sphere with the same volume as the dumbell). The calculated compressibility factors,P/ρkT, together with the second virial coefficients reported by Isihara, have been used in a least squares evaluation of the constants in an equation of state that expresses the compressibility factor as a function of elongation and density. The fitted equation reproduces the virial coefficients to within about 0·2 per cent and the compressibility factors to within about 0·4 per cent. For the limiting case of hard spheres (l= 0) it reduces to the Carnahan-Starling equation. Expressions have been derived for calculating the isothermal compressibility, residual free energy and residual chemical potential from the equation.

ISSN:0026-8976    

DOI:10.1080/00268978000102591

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Two-dimensional N.M.R. spectroscopy is applied to the elucidation of cross relaxation pathways in liquids. The theory underlying two dimensional studies of cross relaxation and of transient nuclear Overhauser effects is developed. The influence of the correlation time of the molecular random process is investigated. It is found that in the limit of short correlation times (extreme narrowing limit) weak negative cross-peaks are observed. However, for long correlation times (spin diffusion limit) strong positive cross-peaks can be obtained. The technique appears particularly promising for the study of cross relaxation in macromolecules. Examples of intra- and intermolecular cross relaxation in the extreme narrowing limit are presented.

ISSN:0026-8976    

DOI:10.1080/00268978000102601

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The structure of thetert-butyl radical has been investigated by means ofab initiorestricted Hartree-Fock calculations using a split-valence basis set augmented by polarization functions. The radical is predicted to have a pyramidalC3vground state geometry with an out-of-plane bending angle ofcirca10°. Ionization potentials calculated in the ΔSCF approximation are in good agreement with the experimental values.

ISSN:0026-8976    

DOI:10.1080/00268978000102611

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The numerical solution of the Ornstein-Zernike equation (OZE) in two dimensions has been a difficult computational problem. We show that the Wiener-Hopf factorization of the OZE results in two coupled integral equations, and that these equations may be simply solved numerically. For surface monolayers, the hard disc system is an important reference, and particular attention is given to its solution.

ISSN:0026-8976    

DOI:10.1080/00268978000102621

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor