AB INITIO CALCULATIONS OF ATOMIC POLAR AND AXIAL TENSORS FOR HF, H2O, NH3, AND CH4

Atomic polar tensors, Ptp, and atomic axial tensors, M$, are calculated ab initio for HF, H20, NH3, and CH, at the SCFlevel of approximation. A variety of formalisms is used. Analytical derivative methods based on coupled Hartree-Fockperturbation theory are used to calculate length and momentum forms of Ptp, P&(b) and P&(r), and to calculate M$.The random-phase approximation is used to calculate length, momentum, and force forms of P&, P$(R), PiB(P), and P&(F),and angular momentum and torque forms of M&, M$f;) and M&(K). Pts and M2B tensors are calculated using a widerange of basis sets, both "conventional" and "polarized in type. tensors are calculated using different gauges and ata variety of origins. The results enable the relative accuracies of calculations using alternative formalisms, basis sets, andgauges to be assessed. Exact Pke and M$ tensors satisfy a variety of sum rules. The degree to which such sum rules aresatisfied is also used to assess the relative accuracies of alternative procedures for the calculation of Pks and M$ tensors.Our results provide a basis for the choice of optimum calculational procedures in predicting Pts and M2B tensors of moleculesand, thence, their vibrational absorption and circular dichroism spectra.