摘要:

An adiabatic separation is used in conjunction with the method of hyperspherical harmonics to calculate the ground state energy of the three body coulomb systeme+e+e-. The first order correction to the adiabatic approximation is evaluated so as to assess the validity of this approach. The convergence of the energy and the adiabatic potentials at different values of the radial coordinates is investigated.

ISSN:0026-8976    

DOI:10.1080/00268978600100001

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We have carried out non-equilibrium molecular dynamics simulations of a model diatomic molecular liquid subjected to an oscillatory shear perturbation. In two series of simulations we examine the effects of applying the perturbation to the centres of mass of the molecules and to the constituent atoms. The responses in the microscopic stress and the molecular orientation are observed. The differences in the results of applying the two types of perturbation are seen to vanish at low frequencies, as expected, and they do not affect the extrapolation to zero frequency, which adopts a square-root cusp form as seen in atomic systems. However, the differences between ‘atomic’ and ‘molecular’ experiments are quite clear in the moderate- and high-frequency regions. A simple projection operator description, with a single non-analytic stress memory function, is shown to be insufficient to explain the relative magnitudes of the cusps in the stress and orientation responses.

ISSN:0026-8976    

DOI:10.1080/00268978600100011

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Three-body contributions to the van der Waals interaction potential for the ground state of the neon trimer are evaluated using the matrix Hartree-Fock model. Calculations are performed for two classes of nuclear geometries: (a) an equilateral triangle (D3h) with sides of 5·00, 5·25, 5·50 and 5·75 bohr; (b) an isosceles triangle (C2v) with two sides of 5·5 bohr and various angles between them. The site-site function counterpoise correction and the pairwise additive function counterpoise correction are used to investigate basis set superposition effects. The Axilrod-Teller triple-dipole term and higher-order non-additive dispersion terms are determined and compared with the non-additive matrix Hartree-Fock interaction energies for the range of nuclear geometries considered.

ISSN:0026-8976    

DOI:10.1080/00268978600100021

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Following Kramers, we describe the dynamics of an isomerization reactionA⇆Bas a diffusion process in a bistable intramolecular potential. In order to calculate the chemical relaxation timetr, we rely on a purely equilibrium approach, introduced by Chandler, and we focus on the properties of the time correlation functionC(t) = ⟨δNA(0) δNA(t)⟩, and of its derivatives. A plateau formalism permits the extraction of the long relaxation timetrfrom the short time dynamics of a molecule which starts att= 0 from the activated region betweenAand B. The calculation makes it possible to encompass in a unified way the low and high friction limits, which are usually treated differently. It involves the definition of a species specification function σA, which indicates microscopically if a molecule isAorB. Most of the time, σAis taken as a Heaviside function, although its definition should be experiment-dependent. We examine the possibility of taking a wide species specification, presenting a smooth variation in the activated region.

ISSN:0026-8976    

DOI:10.1080/00268978600100031

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Single crystal E.P.R. of Cu(II) in a very low symmetry ligand field is reported. The63Cu hyperfine andgfactors are found to be orthorhombic withgxx= 2·1009,gyy= 2·0811,gzz= 2·3919,Axx= 21·4 ± 0·4,Ayy= 10·0 ± 0·4,Azz= 108·0 ± 0·1 × 10-4cm-1. The magnitude of the principal values of the hyperfine tensor is one of the lowest ever reported for Cu(II) and is rationalized in terms of a mixeddx2-y2/dz2ground state. The 20 K optical bands have been assigned based on RT polarization characteristics and assumingCssymmetry for convenience.

ISSN:0026-8976    

DOI:10.1080/00268978600100041

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Binary fluid ‘Lennard-Jones-mixtures’ of type (μ = σ22/σ11, μ12= σ12/σav12, ν = ϵ22/ϵ11, ν12= ϵ12/ϵav12) with σav12and ϵav12being the arithmetic mean of the corresponding parameters for the like interaction have been studied by molecular dynamics simulations. Similar to a recent work, the static and dynamic cross correlation were determined as a function of the cross parameter ν12. However, in the present investigation the ‘volume parameters’ for the two kinds of particles were different. For this type of mixtures (μ > 1) the border line between stable and unstable systems was found to be at much lower ν12-values than for systems composed of particles of like size (μ = 1·0). The magnitude of the cross correlation agrees however for both types of mixtures. By means of the present systems fluid-fluid phase separation could also be simulated. The system (1·3, 1·05, 2·0, 0·575) shows an inhomogeneous region aroundT* = 3·0 and at pressures of 1500 bar and becomes homogeneous forT* > 4·0.

ISSN:0026-8976    

DOI:10.1080/00268978600100051

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Polyatomic vibrational effects on electron-molecule scattering have been studied by approximate Hartree-Fock calculations in the first Born approximation on the normal vibrational modes of H2O in the ground state. The harmonic and anharmonic effects, which are discussed in detail are small, lending credence to the practice of comparing cross sections calculated at a fixed geometry with (averaged) experimental data.

ISSN:0026-8976    

DOI:10.1080/00268978600100061

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The naive estimation of errors in averages obtained from molecular simulation calculations may lead to serious underestimates due to the strong correlations that usually exist within the series. A commonly employed procedure to overcome this difficulty is to estimate the error from the deviation in the averages over subseries that are considered uncorrelated. However, without knowledge of the correlation the choice of the number of subseries cannot be soundly based. A method to estimate the statistical error using the correlation explicitly without serious additional computational effort and without the need for a tedious examination of the correlation behaviour itself is presented. Results of a test of this method for a molecular dynamics study on the polarization energy of xenon in liquid water are given and a comparison is made with the procedure based on subaverages and with a recently suggested method by Smith and Wells [1].

ISSN:0026-8976    

DOI:10.1080/00268978600100071

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In computer simulations the wavevector-dependent dielectric constant ϵ(k) may be calculated from the equilibrium fluctuations of the spatial Fourier components of the instantaneous polarization of the sample. It is shown that this relationship depends on the boundary conditions/dipolar interactions used in the simulation, not only at infinite but also at finite wavelength, and explicit expressions are given for all simulation techniques currently used. By means of these fluctuation formulas it is now possible to calculate the entirek-dependent dielectric constant from simulations with arbitrary boundary conditions. The formulas also permit a general discussion of the relative merits of various simulation techniques as well as of some quantitative aspects of the Ewald sum in particular.

ISSN:0026-8976    

DOI:10.1080/00268978600100081

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An artefact of simulating diffusion-controlled reactions with a discrete time-step, which arises from lack of knowledge of the trajectory within the time-step, is discussed. A method of interpolating the trajectory to arbitrary accuracy is derived and the interpolated ‘brownian bridge’ process is used to calculate the probability that reaction has occurred during the time-step given the initial and final positions of the particles.

ISSN:0026-8976    

DOI:10.1080/00268978600100091

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor