Pseudo-π currents: rapid and accurate visualisation of ring currents in conjugated hydrocarbons

An inexpensive method for accurate simulation of π contributions to ring currents is proposed. A conjugated carbon framework is formally replaced by a set of hydrogen atoms bearing single 1s (STO-3G) orbitals. Calculation, with the ipsocentric CTOCD-DZ method, of the in-plane σ current density induced by a perpendicular magnetic field then gives a close numerical match to the out-of-plane π current density of the original carbon system at a height of 1 bohr. This ‘pseudo-π’ method depends on the one-to-one correspondence in symmetry between σ and π orbitals and is capable of reproducing the general pattern of π current, its specific features and its orbital decomposition for polycyclic hydrocarbon systems.