Investigation on the computation of atomic multipole moments with the modified cumulative potential-derived semiempirical method

The suitability of calculating atomic multipole moments from AM1 wave functions by cumulative potential-derived method has been investigated. It is shown that this method has a faster convergence of the fitting process and gives a better description of the charge distribution than the original PD method. Atomic charges obtained in this way are of comparable quality with 6-31G* data and the calculated dipole moments are closer to the experimental data than the values computed directly from the AM1 charges. The results demonstrate that the atomic multipole moments higher than monopole moment can be used to supplement the atomic charge to obtain a more accurate description of charge distribution. For the sake of comparison, both the Williams fitting potential surface and the Connolly one are used in the calculation.