摘要:

A double perturbation method is proposed for the calculation of molecular energies over a whole range of internuclear separations. An expression is derived which gives the energy in terms of atomic energies together with energy contributions from the ligands. The energy is written in a form which enables calculations to be performed on a whole sequence of iso-electronic molecular species. The method is specifically aimed to deal with those symmetrical molecules which contain one heavy atom surrounded by a number of identical lighter atoms. As an illustration of the general formalism the ground state of two-electron diatomic ions is considered.

ISSN:0026-8976    

DOI:10.1080/00268977100101921

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Using a form of double perturbation theory we present results of calculations on the ground state energies for the diatomic systems H2+, HHe2+, H2and HHe+. For the homonuclear systems the energy values are unexpectedly good. For the heteronuclear cases the results are very encouraging and lead to optimism about the application of the method to larger systems which contain one heavy atom.

ISSN:0026-8976    

DOI:10.1080/00268977100101931

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The thermal angular motion of a classical linear rotator in an octahedral field with eight wells is studied both analytically and numerically. The strength of the coupling with the thermal bath is introduced. It is shown that in the deep-well case, for a coupling of intermediate strength, the ‘nex-twell-jump’ hypothesis is fulfilled and an absolute value can be calculated for the long-time exponential decay of the angular time correlation functions. The short-time behaviour of these functions reflects damped librations in the wells. The numerical simulation employs random torque impulses to represent the coupling with the thermal bath. For different values of the two parameters of the model (depth of the wellsVand mean interval τibetween torque impulses), the complete correlation functions and the corresponding spectra are computed. The results are compared with experimental data bearing on matrix-isolated molecules, ‘plastic crystals’ and liquids.

ISSN:0026-8976    

DOI:10.1080/00268977100101941

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A simple model, consisting of ‘two-body’ reactant and product trajectories joined by an instantaneous switch, is proposed for the alkali atom-alkyl iodide rebound reactions. The electronic potential surfaces governing these trajectories are justified in terms of the electron jump model. Encouraging overall agreement is found with extensive molecular beam data for the K, Cs + CH3I reactions.

ISSN:0026-8976    

DOI:10.1080/00268977100101951

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

One of the difficulties associated with the transcorrelated method is that the hamiltonian C-1HC is not hermitian, and so energies calculated through ⟨ΦC-1HCΦ⟩/⟨Φ|Φ⟩ are not bounded. Hence, unlike variational methods, when the transcorrelated equations are solved there is no visible monotonic convergence of any quantity. Here it is proposed that the parameters associated with the correlation part ofCshould be determined through the minimization of the transcorrelated varianceUTC=⟨{(C-1HC-W)Φ}2⟩, the orbital parameters ofCand Φ being determined by established methods. No integrals more difficult than 9-dimensional integrals are needed, and if they can be evaluated or approximated in some way, all the parameters ofCΦ can be determined through minimization procedures for any molecule. Calculations on helium are reported which certainly demonstrate the applicability of the method. As in other calculations which minimize variance, the associated energies are not quite so accurate as those when the more direct bi-variational equations are solved, but the difference is insignificant compared to the advantage of having a minimization criterion.

ISSN:0026-8976    

DOI:10.1080/00268977100101961

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

An indirect second-order effect occurs between the methylene-group protons of a radical created by gamma irradiation in a 1, 2, 4-triazol single crystal; this gives a non-crossing phenomenon which is observed on the ENDOR transitions. It is necessary to take this into account in the expression for the transitions, which then allows us to determine the hyperfine tensors of the two protons. Moreover, the presence of this effect helps in the identification of the transitions and the signs of the couplings.

ISSN:0026-8976    

DOI:10.1080/00268977100101971

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Chandler, Weeks and Andersen have recently developed a successful perturbation theory of liquids. In their theory, the radial distribution function of the reference fluid is calculated from that of the hard-sphere fluid. In their published work, the Percus-Yevick theory is used to calculate the hard-sphere radial distribution function. In this paper, the Percus-Yevick theory is used to calculate directly the thermodynamic properties and radial distribution function of the reference fluid. If the Carnahan and Starling averaging procedure is used, the Percus-Yevick thermodynamic properties are excellent. However, the radial distribution function shows the same discrepancies as that of Chandler, Weeks and Andersen. Finally, recent calculations of Chandler, Weeks and Andersen, using the Monte Carlo estimates of the hardsphere radial distribution function are shown to give good results for the reference fluid distribution function. This indicates that the Percus-Yevick theory, rather than fundamental errors in the Chandler, Weeks and Andersen theory, is responsible for the discrepancies.

ISSN:0026-8976    

DOI:10.1080/00268977100101981

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The result of Lee and Yang for the free energy of a square two-dimensional Ising model in a magnetic field of ½iπ is shown to be correct only if the thermodynamic limit is approached through even numbers of lattice sites. Derivations of this result are given by the algebraic (Onsager-Kaufman) method and the fermion operator (Hurst) method.

ISSN:0026-8976    

DOI:10.1080/00268977100101991

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The purpose of this paper is to derive an expression for the energy transfer probability that differs from that of Förster and Dexter in that it can be used explicitly for discussing the effects of deuteration and temperature on the rate of energy transfer, and the relation between the energy gap of the donor and acceptor molecules and the rate of energy transfer. It is found that, as in radiationless transitions, the temperature dependence of the rate of energy transfer can be expressed as

ISSN:0026-8976    

DOI:10.1080/00268977100102001

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The shape of the vibrational envelope of an absorption band in the solution spectrum of a helical polymer is related to the shape of the corresponding band in the monomer. The approximation used is expected to be valid in both the strong and weak coupling limits. In the strong coupling limit it is shown that under certain conditions the polymer band consists of an extremely narrow peak shifted from the monomer line, as has been observed in the spectra of some cyanine dyes. The identification of this peak with absorption by a propagating exciton mode is supported by a calculation of the effective distance of excitation transfer as a function of coupling strength.

ISSN:0026-8976    

DOI:10.1080/00268977100102011

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor