Delocalized magnetic currents in benzene

Abstract

Results of ab initio calculations of the magnetic properties of cyclic, conjugated hydrocarbons are analyzed for the delocalized current. They fit well into earlier models for localized and delocalized currents, suggesting that an important delocalized current exists, this being due, particularly, to the π electrons. A rigorous definition of delocalized current is proposed. This is achieved by considering the current contribution from each natural orbital, which is conserved (divergenceless, in a stationary problem) when the exchange currents are included. It is argued that these conserved orbital currents should be preferred for the analysis of the induced current density. The delocalized current now defined may be related to the ring current introduced in the context of semiemperical theories. The results of this paper appear to give substance to the conventional ring current ideas, a conclusion which is at variance with the most recent interpretations of the new ab initio calculations.