BASIS SET AND GAUGE DEPENDENCE OF ABINITIO CALCULATIONS OF VIBRATIONAL ROTATIONAL STRENGTHS

Calculations of vibrational rotational strengths using Stephens' equation are reported for six small chiral organic molecules: hydrazine, trans-1,2-dideuteriocyclopropane, fluorohydroxylamine, propane-1,1,1-d3-2-d1, carbodiimide, and oxaziridine. Atomic polar and axial tensors are calculated ab initio at the SCF level of approximation using analytical derivative techniques. The dependence of atomic polar and axial tensors and of dipole and rotational strengths calculated thence on the basis set and (in the case of atomic axial tensors and rotational strengths) gauge is examined. The common origin gauge leads to origin-dependent rotational strengths, while the distributed origin gauge yields origin-independent rotational strengths. The basis set dependence of the origin dependence of common origin gauge rotational strengths is also examined. Exact atomic polar and axial tensors are interconnected via a sum rule. The basis set and gauge dependence of the degree to which this sum rule is satisfied are also examined. It is found that the distributed origin gauge is substantially more accurate than the common origin gauge. The atomic polar and axial tensors obtained for cyclopropane are compared with recent RPA calculations of Lazzeretti et al. The dipole and rotational strengths obtained for trans-1,2-dideuteriocyclopropane are compared with recent experimental spectra of Nafie and co-workers. © 1990 American Chemical Society.