摘要:

Gibbs ensemble Monte Carlo simulations are reported using a Keesom-like potential for the vapour-liquid phase coexistence of both pure fluids and binary mixtures containing a dipolar component. The coexistence properties and critical points were determined for dipolar strengths of μ*2= 0, 1, √2 and 2. Comparison with simulations from the Stockmayer potential indicate that the Keesom potential is a reasonably accurate alternative when μ*2⩽ 1>. The effect of long-range dipole interactions is to restrict the extent of two-phase equilibria that would be otherwise induced by the dipole. The vapour-liquid equilibria of binary mixtures containing non-polar, two dipolar (μ1*2= 1; μ2*2= 1) and non-polar plus dipolar (μ1*2= 0; μ2*2= 1) components are investigated. The extent of vapour-liquid equilibria can be enhanced substantially by dipolar interactions.

ISSN:0026-8976    

DOI:10.1080/00268979600100661

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We have computed the fourth virial coefficient of a binary mixture composed of different-sized hard discs and hard spheres with additive diameters. The irreducible cluster integrals were evaluated numerically using the Monte Carlo method.

ISSN:0026-8976    

DOI:10.1080/00268979600100671

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The crystal structure of dichlorofluoromethane or freon 21 (CHFCl2) has been determined at temperatures ranging from 5 K to 105 K using neutron powder profile techniques. There is only one phase present at all temperatures, with eight molecules per unit cell positioned on general sites in the space group Pbca. Starting positions and orientations of the molecules were determined to high accuracy using an energy minimization process with atom-atom potentials. Coulombic interactions, as represented using atomic charges, were shown to be unimportant in determining the structure.

ISSN:0026-8976    

DOI:10.1080/00268979600100681

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The structure of fluoroform, CHF3, was determined at 4·2, 40 and 70 K using neutron powder profile analysis. There is only one phase with a monoclinic space group P21/c. At the lowest temperature the lattice parameters are:a= 4·7561(1) Å,b= 6·6280(2) Å,c= 8·5232(2) Å β = 122·02(2)°. Starting positions and orientations of the four molecules in the unit cell were determined to high accuracy using an energy minimization process with atom-atom potentials. The structure is made up of weakly hydrogen bonded sheets with adjacent sheets related by centres of symmetry.

ISSN:0026-8976    

DOI:10.1080/00268979600100691

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The dynamics of orientationally disordered crystals, such as neopentaneC(CH3)4, couple translational and orientational variables in a complex way. From the results of a molecular dynamics simulation of the orientationally disordered phase of neopentane, simple geometrical methods are used to define functions that can be displayed on a two-dimensional surface and yield practical information, and from these are obtained the single-molecule orientation-translation coupling, the coupling between the translation of a molecule and the orientation of one of its neighbours, and the orientation-orientation coupling of two neighbouring molecules. The single-molecule orientation-translation term, although weak, is consistent with experimental results. A distinct orientation-orientation coupling is visible when a C-C bond of one molecule points at a neighbouring molecule, while a bond of that neighbour points away from the former. Isotropy around the connecting vector tends to disqualify pseudospin-type models for neopentane. The most salient feature, however, is the strong two-molecule orientation-translation correlation, which confirms the motion of one molecule when a C-C bond of one of its neighbours points in its direction; up to now this was only inferred from partial experimental data. Predictions are made for the type of information that is likely to be obtained from neutron diffuse scattering.

ISSN:0026-8976    

DOI:10.1080/00268979600100701

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Use is made of the definition of the mean electrostatic potential in terms of the direct correlation functions or radial distribution functions to derive some general results for the single restricted primitive model electrolyte. The implications are considered for a class of screened mean electrostatic potentials which are linear in charge and encompass the Debye-Hückel theory with size, the mean spherical approximation and the linear modified Poisson-Boltzmann theory. In particular, a direct correlation function is derived for the Debye-Hückel theory with size.

ISSN:0026-8976    

DOI:10.1080/00268979600100711

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A modified Poisson-Boltzmann theory is used to analyse the steric effects of the solvent in the electrical double layer by considering a mixture of charged and uncharged hard spheres moving in a dielectric continuum near a plane charged wall. The uncharged system is described by Bogoliubov-Born-Green-Yvon theory. A comparison with preliminary Monte Carlo results implies that the theory gives qualitatively correct results for 1 : 1 electrolytes up to moderate electrolyte concentrations and surface charge, using a typical liquid density for the uncharged solvent. Comparisons are also made with some density functional results for 1:1 and 2:2 electrolytes.

ISSN:0026-8976    

DOI:10.1080/00268979600100721

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We report an extension of Lekner's method (Lekner, J., 1991PhysicaA,176,485) for charge summation in quasi-two-dimensional simulations for the general case where the simulation cell is rectangular rather than square. The equations developed here for the force components and the potential energy can be included easily in molecular dynamics or Monte Carlo simulations of layers or quasi-two-dimensional confined systems which contain charged species.

ISSN:0026-8976    

DOI:10.1080/00268979600100731

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The infrared spectrum of the weakly bound complex Ar-CO has been studied in the 4·7 μm region of the CO stretching vibration by means of three complementary techniques: a continuous slit-jet supersonic expansion with a tunable diode laser, a long-path cooled cell with a tunable diode laser, and a long-path cooled cell with a Fourier transform infrared spectrometer. Previous studies have characterized states of Ar-CO withKavalues up to 3 in the ground bending state, and up to 1 in the first excited bending state. Here these studies are extended up toKa= 6 by analysing subbands withKa= 4 ← 3, 3 ← 4, 5 ← 4, and 6 ← 5, and thereby obtaining subband origins, rotational parameters, and centrifugal distortion parameters which characterize these states. The results illustrate the relative stability and regularity of high-K(propeller) states, even if on close examination they are subject to perturbations, as compared with excited bending (windmill) and van der Waals stretching states in weakly bound T-shaped complexes.

ISSN:0026-8976    

DOI:10.1080/00268979600100741

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

New model potentials are constructed for Na+-H2O and H2O-H2O, using quantum mechanical calculations of the monomer wavefunctions. One parameter in each model potential is fitted to experimental dimer properties. The resulting Na+-H2O potential is consistent with published thermodynamic andab initiodata, and the H2O-H2O potential reproduces the structure and energy of the water dimer at equilibrium, and the second virial coefficient of steam, within experimental uncertainties. The donor-acceptor interchange tunnelling pathway on the water dimer potential energy surface has a lower energy barrier than the acceptor-acceptor interchange, in agreement with recent spectroscopic studies. When a simple non-additive induction potential is included, calculated thermodynamic properties of solvated sodium ions are in agreement with experimental data. For small clusters in the gas phase, the first solvation shell of the sodium ion is predicted to contain four water molecules.

ISSN:0026-8976    

DOI:10.1080/00268979600100751

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor