摘要:

Various types of 2,3- and 1,2-benzo-substituted zinc-phthalocyanines were prepared to investigate the influence of the substitutions on the electronic states of phthalocyanine (Pc) compounds. The experimental data showed that these compounds can be categorized by their spectral patterns. A simple perturbation method based on the group theory (symmetry-adapted perturbation method) is presented to analyse the spectroscopic changes of Pc compounds caused by the substitutions. This method was tested against the experimental data and gave good agreement.

ISSN:0026-8976    

DOI:10.1080/00268979300102141

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The effect of association on chain molecules is studied, and we consider the case of an associating homonuclear disphere fluid as an example. Monte Carlo simulation results of associating hard disphere and Lennard-Jones (LJ) disphere fluids are presented. We consider the molecules to have one association site placed along the molecular axis. For associating LJ dispheres we investigate the effect of bond length on the properties of the molecule. We extend a theory for associating spherical molecules to chain molecules. The agreement between molecular simulation results and predictions from theory is good. We explain the approximations used to simplify the theory and show how a spherical reference can be used to predict the properties of an associating chain fluid.

ISSN:0026-8976    

DOI:10.1080/00268979300102151

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The anisotropic couplings obtained from the1H nuclear magnetic resonance (NMR) spectra of partially oriented molecules with internal rotation are difficult to analyse because the order parameters for each conformer cannot be deduced without assumptions. The purpose of this paper is to show how a model for the anisotropic short-range potential can be useful in the interpretation of the high-resolution1H NMR spectra of the flexible molecules furfural, 2-chlorobenzaldehyde, and 2,2′-dithiophene dissolved in a 55% Merck ZLI 1132-45%N-(p-ethoxybenzylidene)-2,6-dideutero-p'-n-butylaniline (w/w) mixture. In this nematic mixture there is no contribution to the anisotropic potential from the interaction between the solute molecular quadrupole moment and the average electric field gradient of the liquid crystal solvent; the dominant anisotropic intermolecular potential in this mixture is taken to result solely from short-range interactions. We find good agreement between experiment and the order parameters calculated by the model of short-range interactions. The ratios of order parameters for the s-cisand s-transconformers predicted by the model are used to calculate the statistical weights of the s-transconformation for the solutes: at 304 K,ptrans(furfural) = 0·45 ± 0·02,ptrans(2-chlorobenzaldehyde) = 0·901 ± 0·006 andptrans(2,2′-dithiophene) = 0·6094 ± 0·0008.

ISSN:0026-8976    

DOI:10.1080/00268979300102161

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Double perturbation theory is used for calculating the correlation energy in localized representation. Incorporating the single-particle part into the zeroth order Hamiltonian leads to recovery of the ‘ordinary’ many-body perturbation theory (MBPT) in the canonical representation. This means that in the localized representation we sum over the single particle part in infinite order; the results approach the corresponding canonical ones. In this paper it is shown that taking the sum to second order in the localization correction gives results very close to the second order canonical correction (MP2), and the results obtained at the third and fourth levels are also investigated (MP3 and MP4, respectively). The convergence of the localized representation is affected by the localizability of the canonical orbitals. We have shown that the conventional localization procedure of Boys is suitable for our purpose: the CH4molecule has been studied using large basis sets as well.

ISSN:0026-8976    

DOI:10.1080/00268979300102171

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The nuclear shielding constants and their change in the presence of an external uniform electric field are investigated for H2, N2, HF, and CO. The relevant properties are calculated analytically at the self-consistent field (SCF) level of approximation. Particular attention is paid to the choice of basis sets and gauge variance, both of which are measured by the satisfaction of certain sum rules. These calculations of electric field dependence are more accurate than those presented hitherto and, in the case of N2, are the first to be published.

ISSN:0026-8976    

DOI:10.1080/00268979300102181

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The nuclear magnetic shielding σ in a molecule is changed by the presence of an external uniform electric field. This change may be expressed in terms of the shielding polarizabilities σ′ and σ″. Values of σ′ and σ″ have been evaluated for H2, N2, HF and CO using a combination of the second order Møller-Plesset theory (MP2) and the finite-field perturbation theory. The effects of electron correlation on the σ′ and σ″ tensors for N2, HF and CO are seen to be sufficiently large that a higher-order theory than MP2 will be necessary to account for them fully.

ISSN:0026-8976    

DOI:10.1080/00268979300102191

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In a closed-shell self-consistent field calculation on a molecule without symmetry the number of degrees of variational freedom is equal to the product of the dimensions of occupied and virtual spaces. It is shown that this relation also applies within each irreducible representation in the case where the molecule has symmetry, and that it can be generalized to open-shell and many-shell cases. Illustrative examples for large, highly symmetric molecules show that extensive variational freedom can persist even in minimal basis sets.

ISSN:0026-8976    

DOI:10.1080/00268979300102201

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268979300102211

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In irreversible thermodynamics it is assumed that dissipative systems can be described by taking either the thermodynamic force or the thermodynamic flux as an independent state defining variable. Similarly in electric circuit theory it is assumed that any circuit can be represented by either a Norton (constant current) or a Thévenin (constant voltage) equivalent circuit. In this paper we sketch a statistical mechanical proof of this equivalence.

ISSN:0026-8976    

DOI:10.1080/00268979300102221

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor