AB-INITIO CALCULATIONS OF MAGNETIC-SUSCEPTIBILITIES ON HF, H2O, CH4 AND NH3 COMPOUNDS EMPLOYING THE GEERTSENS GAUGE-INDEPENDENT METHOD

Geertsen (J. Geertsen, J. Chem. Phys., 90 (1989) 4892; Chem. Phys. Let t., 179 (1991) 479; 188 (1992) 326) proposed a polarization propagator based theory for calculation of the diamagnetic contribution to the m agnetic susceptibility. The translational gauge invariance of the magn etic properties is used here to obtain these diamagnetic contributions in terms of the force and the position operators in addition to that of the velocity operator proposed by Geertsen. Accurate calculations o f the magnetic susceptibility on HF, H2O, CH4 and NH3 compounds perfor med for these additional formalisms, found by very general quantum-mec hanical relations, demonstrate that when the force or the position ope rators are used instead of the velocity one, the required invariance o f the magnetic susceptibility depends on the fulfillment of very gener al gauge-invariant sum rules.