THE USE OF LOCALIZED MOLECULAR-ORBITALS AND THE POLARIZATION PROPAGATOR TO IDENTIFY TRANSMISSION MECHANISMS IN NUCLEAR SPIN-SPIN COUPLINGS

An extension of the IPPP (inner projections of the polarization propagator) method to theoretically analyze transmission mechanisms of indirect nuclear spin‐spin couplings is presented. The localization technique used is modified so that all the canonical molecular orbitals of a compound may be localized to represent chemical bonds, lone pairs, and the corresponding antibonding molecular orbitals. These localized molecular orbitals, together with the polarization propagator, are used to obtain an intuitive picture of how a coupling is generated as a sum of terms, each one consisting of two particle‐hole single excitations. This picture can be used to identify underlying transmission mechanisms and quantitatively evaluate their importance toward the total coupling. The paramagnetic spin‐orbit and the spin‐dipole interactions are studied in detail. Copyright © 1990 John Wiley & Sons, Inc.