ISSN:0026-8976    

DOI:10.1080/00268978400102091

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Some simple theories are described for calculating rate constants for neutral chemical reactions in the gas phase which are dominated by long-range forces and have no barriers in the potential energy surface. The methods involve combining an adiabatic capture approach with the quantum mechanical sudden approximation of non-reactive energy transfer. A version of the technique is shown to work well in calculations on the O + OH reaction. The methods are applied to the diatom-diatom reactions SO + OH, NO + BrO, NO + ClO, CN + O2and CH + O2. The results provide new information on the origin of the negative temperature dependence of the rate constants for reactions such as these.

ISSN:0026-8976    

DOI:10.1080/00268978400102101

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The electronic structure of the hexafluoride anions of the first (Ti-Zr) and second (Zr-Cd)d-metal is calculated using the discrete variationalXα-method. An analysis of the electronic structure peculiarities is based on the comparison of the valence MO compositions. It is concluded, that all the hexafluorides of the 3dand 4dmetals may be considered as superhalogens. The EA values of neutrals are related to the character and structure of the highest occupied MO of the corresponding anions.

ISSN:0026-8976    

DOI:10.1080/00268978400102111

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Molecular dynamics (MD) calculations were performed for a Lennard-Jones fluid system over a wide density range. Pair correlation functions and potential energy fluctuations and to a lesser extent potential energy distributions have been determined. The analysis of potential energy of the system was done in terms of the mean standard deviations of the repulsive, attractive and total contributions separately. The results are as follows: (i) the range of validity of first order perturbation approaches such as that of Weeks, Chandler and Andersen (WCA) can be predicted quantitatively; (ii) the frequently used picture of a uniform ‘background potential’ is precisely supported for a surprisingly large density range; (iii) simple, physically plausible extensions of the WCA approach for a larger density range could not be extracted; (iv) anad hoccorrection of the WCA treatment predicts however the pair correlation functions in agreement with MD-results for a reduced density range of 0·15 ⩽ ρ* ⩽ 0·65 to better than 6 per cent at temperatures of 120–200 K. The correction term is easy to compute.

ISSN:0026-8976    

DOI:10.1080/00268978400102121

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Two simple models for the prediction of pair correlation functions in binary mixtures from pure fluid information, i.e. the van der Waals 1-approximation and the mean density approximation, are investigated by numerous comparisons with computer simulations for the Lennard-Jones (12-6) potential. In particular, important integrals over the pair-correlation function, that arise in thermodynamic perturbation theory as well as in transport theory, are evaluated. An empirical modification of the mean density approximation is established which gives quite reliable values for these integrals even for systems with large ratios of the potential parameters.

ISSN:0026-8976    

DOI:10.1080/00268978400102131

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Expressions are given for the matrix elements of one- and two-electron operators between determinants composed of non-orthogonal orbitals, in the case (relevant to perturbation theory) where the determinants are obtained by single or double replacement of orbitals in a reference determinant. The matrix elements can all be expressed in terms of cofactors of the overlap matrix of the orbitals contained in the reference determinant.

ISSN:0026-8976    

DOI:10.1080/00268978400102141

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A perturbational method is described for calculating the interaction energy of two molecules in the region where the overlap between their wave-functions is significant. By working directly with a basis of determinants constructed from the SCF orbitals of the separated molecules, without orthogonalization, it is possible to avoid many of the disadvantages of other methods.

ISSN:0026-8976    

DOI:10.1080/00268978400102151

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The new intermolecular perturbation theory described in the preceding papers is applied to some van der Waals molecules. HeBe is used as a test case, and the perturbation method converges well at interatomic distances down to about 4a0, giving results in excellent agreement with supermolecule calculations. ArHF and ArHCl have been studied using large basis sets, and the results agree well with experimental data. The ArHXconfiguration is favoured over the ArXH configuration mainly because of larger polarization and charge-transfer contributions. In NeH2the equilibrium geometry is determined by a delicate balance between opposing effects; with a double-zeta-polarization basis the correct configuration is predicted.

ISSN:0026-8976    

DOI:10.1080/00268978400102161

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The relative vibronic intensities of the vibronic orgins due to the three odd parity vibrational modes have been calculated for the2Eg↔4A2gtransition of the octahedral MnF62-ion using a ligand polarization model. It is shown that within this model the relative intensities of the vibronic origins depend only on the vibrational force field and numerical results for six force fields are presented. The absolute intensities depend strongly on the assumed metal radial functions but using functions appropriate to Mn3+or Mn4+fair agreement with experiment is obtained. The combination of the previously calculated crystal field vibronic intensities with these ligand polarization intensities is considered. Cross terms between the two contributions are important, especially if closure is employed in the crystal field calculation.

ISSN:0026-8976    

DOI:10.1080/00268978400102171

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A method to perform molecular dynamics simulations for systems of particles interacting with discontinuous potentials is presented. It is a generalization of Alder and Wainwright's algorithm for potentials represented by an arbitrary number of discontinuous horizontal line segments. The method is applied to several hard molecular fluids of various shapes, discrete Lennard-Jonesium, surfaces and mixtures in order to test its generality and flexibility. Results are compared, when possible, with previously published material, which includes numerical, theoretical and experimental results. These comparisons show that the method is a powerful tool in the study of molecular fluids and looks like a promising alternative approach to perform molecular dynamics for continuous potentials represented by a series of discontinuous line segments. The flexibility of the method will allow the testing of theories based on integral equations, like RISM and RAM, and to develop equations of state for complex hard molecules to be used as reference fluids in perturbation theories.

ISSN:0026-8976    

DOI:10.1080/00268978400102181

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor