Approximate variation-perturbation calculations of second-order molecular properties

Abstract

The variation-perturbation method is applied to the calculation of the magnetic susceptibility of diatomic molecules within the basis of the CNDO/2 SCF wave functions. All the many-centre integrals which appear in the treatment were simplified according to the ZDO approximation. The calculated diamagnetic contribution is in good agreement with non-empirical results. It agrees also with available experimental data. Although the paramagnetic part of the susceptibility tensor was calculated with a simple two-term form of the variational correction, the results are comparable to those obtained in more advanced ab initio treatments. Also the computed total magnetic susceptibility of various diatomic molecules is in substantial agreement with non-empirical results. A comparison is made with the results of other semi-empirical calculations based on the CNDO/2 SCF wave functions. It follows that the results of the present method are remarkably better.