Evaluation of Gaussian basis sets in ab initio

Ab initio wave functions for NH₃ have been calculated using the STONG program, where N is 2 to 6, and with Gaussian 70, employing the 4–31 and 6–31 basis sets. Electric field gradients at the N atom were computed from the gaussian basis orbitals, and, with STONG, also from the equivalent STO's. Results from the two split valence shell Gaussian 70 calculations are in good agreement with values from extended SCF and SCFCI calculations. Because of adequate agreement with more extended calculations, the use of the 4–31 basis set is chosen to calculate field gradients in molecules consisting of five or more second row atoms. It should be adequate for the prediction of the region for searching for new ¹⁴N, ¹⁷O and ²H NQR spectra. An improved value of the electric quadrupole moment for the ¹⁴N nucleus is proposed.