Extension of the PM3 method on s,p,d basis. Test calculations on organochromium compounds

A model for estimation of the two-electron interaction in molecules is proposed. It is based on the bipolar expansion of the Ohno potential which is considered as a universal effective potential of the two-electron interaction. It allows to estimate efficiently the two-electron fockian terms taking into implicit account the dynamic electron correlation. The formulas obtained do not depend explicitly on the orbital quantum number of the basis AO's, and this approach may be used to extend the semiempirical NDDO-type methods to the s,p,d basis. In this work, this approach was applied to the semiempirical PM3 model, and the test calculations were performed on organochromium compounds, taking into explicit account the chromium d orbitals. The calculated thermodynamic, structural, and electron properties of above 30 organochromium compounds of different classes (sandwich complexes, carbonyls, nytrosyls, and mixed derivatives) stay in good agreement with the experimental data.