New Schemes for Calculation and Analysis of Properties

Zhou and Dykstra have carried out large basis set ab initio calculations on a large set of organic molecules and attempted to analyse the dipole polarizability and second hyperpolarizability in terms of additive and transferable atomic contributions. Reasonable estimates of the appropriate tensor average properties can be obtained, although the agreement for f is worse than for a, but individual tensor components are poorly reproduced. 

Bishop and Bouferguene have also attempted to partition molecular polarizabilities and hyperpolarizabilities into localized group contributions over the molecular frame. The theory has been applied to a series of push-pull polyenes. An interesting conclusion is that there is little similarity between the distributions for the vibrational and electronic contributions. 

McCoy and Sykes have introduced a method based on Fourier fransforming the ab initio wavefunction to generate a momentum space representation. Low momentum components of this function are then fitted to known values of the property under consideration for a series of molecules enabling the corresponding property of other molecules to be obtained by interpolation. 

Hohn has reviewed some of the aspects of polarizability in the light of new experimental and theoretical methods. 

Kuzyk has attempted to find upper limits for molecular hyperpolarizabilities. He argues that application of sum rules to the three level model enables one to prove that the two-level limit yields the absolute maximum susceptibihty, which depends only on the first excited state transition energy and the number of electrons. This conclusion has been tested by showing that a large set of experimental P and y values never exceed these limits. The conclusions are very far reaching and if confirmed will have important consequences for the future direction of research in this field. 

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New Schemes for Calculation and Analysis of Properties. - Jonsson, Ruud and Taylor have described aspects of the paraUehzation of the DALTON quantum chemistry program in relation to its application to the calculation of the second and higher order properties of large molecules. 

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