Method/basis set dependence of the traceless quadrupole moment calculation for N2, CO2, SO2, HCl, CO, NH3, PH3, HF, and H2O

Dipole moments and traceless quadrupole moments for a training set of nine molecules-N-2, CO2, SO2, HCl, CO, NH3, PH3, HF, and H2O-were deduced from the final optimized density matrices of a series of ab initio calculations, thereby employing different levels of theory with varying basis set quality. All the results were obtained in a true ab initio sense, meaning that at a certain combination of method/basis set, the configurations of the molecules were first subjected to a geometry optimization and only afterwards the dipole and traceless quadrupole moments were derived for the final relaxed structures. All results could be compared to experimental data, thus the quality of the different models with respect to applicability and reliability of calculating molecular moments without any knowledge of structural details of the equilibrium geometries could be evaluated. Generally, a combination of methods that take into account correlation effects, together with a high-level basis set, was found to yield molecular moments close to the experimental values. (C) 2002 John Wiley & Sons, Inc.