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

Atomic polar tensors, Pαβλ, and atomic axial tensors, Mαβλ, are calculated ab initio for HF, H2O, NH3, and CH4 at the SCF level of approximation. A variety of formalisms is used. Analytical derivative methods based on coupled Hartree-Fock perturbation theory are used to calculate length and momentum forms of Pαβλ, Pαβλ(μ) and Pαβλ(π), and to calculate Mαβλ. The random-phase approximation is used to calculate length, momentum, and force forms of Pαβλ, Pαβλ(R), Pαβλ(P), and Pαβλ(F), and angular momentum and torque forms of Mαβλ, Mαβλ(L) and Mαβλ(K). Pαβλ and Mαβλ tensors are calculated using a wide range of basis sets, both "conventional" and "polarized" in type. Mαβλ tensors are calculated using different gauges and at a variety of origins. The results enable the relative accuracies of calculations using alternative formalisms, basis sets, and gauges to be assessed. Exact Pαβλ and Mαβλ tensors satisfy a variety of sum rules. The degree to which such sum rules are satisfied is also used to assess the relative accuracies of alternative procedures for the calculation of Pαβλ and Mαβλ tensors. Our results provide a basis for the choice of optimum calculational procedures in predicting Pαβλ and Mαβλ tensors of molecules and, thence, their vibrational absorption and circular dichroism spectra. © 1990 American Chemical Society.