Ring currents and magnetisability in C 60

Abstract

A distributed-origin coupled Hartree-Fock method is used to compute the current density induced in C 60 by an external magnetic field, and hence to plot the π ring currents and obtain ab initio values of the total magnetisability and nuclear magnetic shielding. Paramagnetic ring currents are associated with pentagons, and interpreted as consequences of strong, local circulations about the formal double bonds of the C 60 framework. The calculated total magnetisability of −370 cgs ppm is strongly diamagnetic and in agreement with the previous extrapolated ab initio result and with an experimental measurement. The calculated central shielding of +12 ppm is in qualitative agreement with the previous extrapolation and the measured encapsulation shift for 3He in C 60. It is concluded that C 60 is diagmagnetic, but that the interpretation of this diamagnetism as a sing of three-dimensional aromaticity is problematic.