ISSN:0026-8976    

DOI:10.1080/00268978500102481

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Interaction energies from a CI calculation of NaCl and between the like ions Na+-Na+and Cl--Cl-, previously reported, are accurately fitted to closed analytical expressions. Some qualitative comparisons are presented between the obtained Na+-Cl-potential and other frequently used empirical potentials. The non-empirical quantum mechanical pair-potential is used to calculate vibrational and rotational spectroscopic parameters for the diatomic sodium chloride. Phonon dispersion curves, obtained in inelastic neutron scattering measurements, are calculated within the rigid ion model. In addition we present our computations on the polymorphic transition pressure; several other crystal properties are extracted from the potential function. Also, results of a molecular dynamics study of fused NaCl are presented. The simulated values of the equilibrium and dynamical properties are shown to be in good agreement with the available experimental data. The calculated radial distribution functionsg+ +,g+ -andg- -reproduce the experimentally observed fine structure. The calculated internal energy, however, is 25 per cent lower than the reported experimental zerobaric value. The neglect of many-body effects in the potential is discussed.

ISSN:0026-8976    

DOI:10.1080/00268978500102491

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The relative phases of contributions to the primitive semiclassicalSmatrix arising from different trajectories obeying the appropriate stationary phase conditions are considered for systems with a single internal degree of freedom, such as the case of collinear atom-diatom scattering. It is found that the relative phases are determined by the behaviour of final action and angle functions associated with the internal degree of freedom at points where the action function has an extremum, treating these variables as functions of the initial angle. The time evolution of the action and angle functions throughout the collision process is analysed using classical mechanics. Although the angle function can change discontinuously at specific points, it is demonstrated that the primitive semiclassicalSmatrix varies continuously at these points. It is also shown that certain types of changes in the action and angle functions which would result in a poorly definedSmatrix are precluded by the classical mechanics.

ISSN:0026-8976    

DOI:10.1080/00268978500102501

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The interaction quadrupole-induced dipole correlation function and the corresponding absorption spectrum of liquid nitrogen have been simulated in a site-site molecular dynamics calculation at atmospheric pressure and 66 K. Two models were used: an anisotropic and an isotropic molecular polarizability model. The differences between the two models are significant, but small. The results were compared to the published absorption spectra and reasonable agreement was obtained. The differences between simulation and experiment are discussed in terms of the properties of the model used. The total dipole correlation function was analysed in terms of a self-term and a cross-term. The contribution of the latter, which is negative, is quite large. Furthermore, a number of correlation functions describing the details of the molecular motion in the liquid have been calculated and are discussed in view of a possible discrimination between rotational/translational motions and/or single-molecule/collective motions.

ISSN:0026-8976    

DOI:10.1080/00268978500102511

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A simple model of a binary alloy in a one-dimensional lattice is used to map the phenomena observed in a fluid filling a planar capillary. It is proposed that the presence of oscillating forces acting on the walls is due to the constructive/destructive interference between the local ordering induced by the boundaries. The numerical results agree with the deduced analytical ones and are compared with the reported experimental results.

ISSN:0026-8976    

DOI:10.1080/00268978500102521

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The qualitative theory of level clustering in the rotational spectrum of the cubic symmetry molecules at large angular momenta is built on the basis of approximate methods of solution of three-term recurrent relations (TRR). The discrete quasi-classical approximation and the approximation of the TRR by a second-order differential equation are considered. The analytical expressions for cluster energy and splitting due to tunneling are obtained.

ISSN:0026-8976    

DOI:10.1080/00268978500102531

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A molecular theory for smectic A liquid crystals is described which starts from an expression for the internal energy in terms of the orientational and translational order parameters. This expression is used to determine the single particle distribution function by invoking the molecular field approximation. The relationship of this model to the McMillan theory of smectic A liquid crystals which contains an additional mixed order parameter is explained. The predictions of our theory have been explored for a wide range of the strength parameters occurring in it. The phase diagram which contains isotropic, nematic, smectic A and plastic crystal phases has been constructed and the properties of the smectic A-nematic transition evaluated in detail; these include the second order transition temperatures and tricritical point, the entropy of transition and the change in the order parameters. Such properties, which have been determined both numerically and analytically, are found to be in good agreement with the predictions of McMillan's theory for a wide range of the strength parameters. Finally the analytic results for the smectic A-nematic transition are used to show that this molecular theory cannot on its own, account for the observation of re-entrant nematic and smectic A phases. However we show that re-entrant polymorphism is possible if the strength parameters are allowed to vary with temperature.

ISSN:0026-8976    

DOI:10.1080/00268978500102541

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The spin-coupled valence bond approach to electronic structure is applied to the ground state and low-lying excited states of the LiHe+molecular ion using a universal even-tempered basis set of Slater-type functions. Using just 23 spin-coupled structures, we examine directly the quality of the virtual orbitals for describing the asymptotic separations between the excited states, and find these to be very good.

ISSN:0026-8976    

DOI:10.1080/00268978500102551

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The use of a bond-order-like functional form within the framework of a procedure designed for fitting both experimental andab initiodiatomic data is discussed. The advantage of using such a functional form for describing the two body component of a polyatomic interaction is illustrated. Its accuracy is tested by fitting spectroscopic and scattering information relative to several diatomic systems.

ISSN:0026-8976    

DOI:10.1080/00268978500102561

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A generalization to the triatomic systems of a Bond Order approach developed in the preceding paper for the diatomic molecules is discussed. The new global fitting procedure is first tested against other methods for the H3molecule and then applied to the BeHF system.

ISSN:0026-8976    

DOI:10.1080/00268978500102571

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor