ACCURACY ASSESSMENT OF THE ROHF-CCSD(T) CALCULATIONS OF DIPOLE-MOMENTS OF SMALL RADICALS

Dipole moments of a series of radicals, OH, NO, NS, SF, SO, PO, ClO, C N, LiO, NO2, and ClO2 were calculated by the Coupled Cluster CCSD(T) m ethod with the single determinant restricted open shell Hartree-Fock ( ROHF) reference. For all molecules theoretical dipole moments were car efully compared to experimental values. The size and the quality of th e basis set were systematically improved. Spin adaptation in the ROHF- CCSD(T) method, largest single and double excitation amplitudes and th e T-1 diagnostics were considered as indicators in the quality assessm ent of calculated dipole moments. For most molecules the accuracy with in 0.01-0.03 D was readily obtained. For ClO and CN the spin adaptatio n was necessary - its contribution was as large as 0.03-0.045 D. Large deviation from experiment is observed for OH in its A(2)Sigma(+) exci ted state (0.135 D) and especially for LiO in its (2)Pi ground slate ( 0.22 D). No indication of the failure of theoretical calculations was found which leads to the conclusion that, even if there is still a spa ce for the improvement of theoretical calculations, experimental value s should be reconsidered.