摘要:

An effective pair potential for systems of uniformly charged lamellar colloids in the presence of an electrolytic solution of microscopic co- and counterions is derived. The charge distribution on the discs is expressed as a collection of multipole moments, and the tensors which determine the interactions between these multipoles are derived from a screened Coulomb potential. Unlike previous theoretical studies of such systems, the interaction energy may now be expressed for discs at arbitrary mutual orientation. The potential is shown to be exactly equivalent to the use of linearized Poisson–Boltzmann theory.

ISSN:0026-8976    

DOI:10.1080/002689700417493

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The results are presented of Gibbs ensemble Monte Carlo (GEMC) simulations examining the nematic–isotropic (N–I) coexistence envelope of a liquid crystal mixture. The system studied is a 50:50 mixture of 1000 generalized Gay–Berne particles with axial ratios 2.0:1 and 2.5:1. For this system, stable N–I coexistence is observed over run lengths in excess of 5 x 105GEMC sweeps. There is unambiguous evidence of fractionation, the mole fractions of long particles in the coexisting phases typically differing by 11%. The measured coexistence envelope does not conform to the lens shape predicted by Onsager theory; qualitative finite size arguments are given in explanation of this distortion.

ISSN:0026-8976    

DOI:10.1080/002689700417501

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Symmetry arguments are applied to the determination of closed-form solutions to the classical dipole-induced-dipole model of interaction polarizabilities for polyhedral clusters of cubic and icosahedral symmetry. Analytical conditions for the range of applicability of the model and onset of the ‘polarization catastrophe’ are given. These conditions are expressed as transformed versions of the hyperbolic curve of divergence that is already present in the classical case of an interacting pair. Clusters based on the cube and the icosahedron support unique patterns of induced dipoles, but other physically accessible distributions are found for the octahedron (equatorial dipoles antiparallel to a large central moment), tetrahedron and dodecahedron (central and mean cage dipole moments antiparallel).

ISSN:0026-8976    

DOI:10.1080/002689700417510

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Coriolis interactions in local mode (n100) combination states of GeH4are studied. Three widely used local mode models, the normal mode model with Darling–Dennison resonance included (NMDD) model and the anharmonically coupled anharmonic oscillator (ACAO) model with two different kinds of bond stretching variable, were used to calculate the values of the interaction parameters. As a test of these three models, the Coriolis interaction parameters of the local mode (3100) combination bands of the74GeH4,72GeH4and70GeH4species, recorded at a resolution of 0.015cm-1on a Bruker IFS120HR Fourier transform spectrometer, are compared with the calculated results. There is good agreement.

ISSN:0026-8976    

DOI:10.1080/002689700417529

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

For 30 molecules and two atoms, MPncorrelation energies up ton= 6 are computed and used to analyse higher order correlation effects and the initial convergence behaviour of the MPnseries. Particularly useful is the analysis of correlation contributionsEXY(n)...(n= 4,5,6;X, Y,... = S, D, T, Q denoting single, double, triple, and quadruple excitations) in the form of correlation energy spectra. Two classes of system are distinguished, namely class A systems possessing well separated electron pairs and class B systems which are characterized by electron clustering in certain regions of atomic and molecular space. For class A systems, electron pair correlation effects as described by D, Q, DD, DQ, QQ, DDD, etc., contributions are most important, which are stepwise included at MPnwithn= 2,...,6. Class A systems are reasonably described by MPntheory, which is reflected by the fact that convergence of the MPnseries is monotonic (but relatively slow) for class A systems. The description of class B systems is difficult since three- and four-electron correlation effects and couplings between two-, three-, and four-electron correlation effects missing for lower order perturbation theory are significant. MPnmethods, which do not cover these effects, simulate higher order with lower order correlation effects thus exaggerating the latter, which has to be corrected with increasingn. Consequently, the MPnseries oscillates for class B systems at low orders. A possible divergence of the MPnseries is mostly a consequence of an unbalanced basis set. For example, diffuse functions added to an unsaturated sp basis lead to an exaggeration of higher order correlation effects, which can cause enhanced oscillations and divergence of the MPnseries.

ISSN:0026-8976    

DOI:10.1080/002689700417538

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dependence of several molecular properties (polarizabilities, multipole moments) of adsorbed diatomic molecules on the intramolecular distance are discussed within time-independent perturbation theory. The nearly linear dependence of the intermolecular interaction energy and molecular properties rationalizes the small variation of the property functions compared with those for the gas state. This relative independence of the property functions was demonstrated numerically in a previous paper using an iterative procedure for molecular hydrogen adsorbed in a zeolite-A-type framework.

ISSN:0026-8976    

DOI:10.1080/002689700417547

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/002689700417556

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The ground state structure, singlet excitation energies, transition moments and static dipole polarizabilities together with the Cauchy coefficients are calculated for Li2, Li4and Li8using the coupled cluster response methods. Basis set and correlation effects are investigated for these properties. For the dipole polarizabilities the geometry effects are found to be particularly significant. The computed isotropic static dipole polarizabilities, approximately 209au for Li2, 333au for Li4and 541au for Li8, and the calculated optical properties are generally in good agreement with experiment. For Li8, the results are obtained for the capped centred trigonal prism structure and for the tetrahedral structure. The first of these structures gives a more consistent description of the ground state properties of the cluster.

ISSN:0026-8976    

DOI:10.1080/002689700417565

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Theab initioscalar ZORA approach, which was previously tested within the context of numerical and basis set SCF calculations, is generalized to include electron correlation. The technical details of the method are investigated in calculations on the systems Ne2, Ar2, Kr2and Xe2. For the weakly bonded rare gas dimers we calculated the bond lengths and well depths using the non-relativistic ZORA and scaled ZORA MP2 method. The relativistic effect on the potential energy minimum, obtained with the most accurate method (scaled ZORA) is shown to be very close to that of the Dirac-Fock MP2 method.

ISSN:0026-8976    

DOI:10.1080/002689700417574

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

For many proposed equations of state for fluids composed of chain-like molecules, the compressibility factor is related to the chain number concentration only through the total monomer concentration. For these theories, the virial coefficients do not scale correctly with the chain molecular weight in the long chain limit, which can lead to a poor description of the phase diagram. In addition, for equations of state that are analytical at the critical point, it is found that the critical compressibility factor approaches ⅓ in the limit of infinitely long chains, contrary to experimental trends. Appropriate scaling leads to the proper trend for the compressibility factor, as demonstrated with a simple equation.

ISSN:0026-8976    

DOI:10.1080/002689700417583

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor