Gauge field theory corrections

London orbitals were introduced by Fritz London, who in 1937 used Hiickel theory to calculate the contribution to the magnetizability from the ring currents in the 7r-orbital backbone of some aromatic molecules [13]. The great virtue of London s approach is that each individual AO—the building blocks of molecular wave functions—has been harnessed to respond correctly (to first order at least) to the application of an external magnetic field, irrespective of the choice of the external gauge origin. Moreover, since, in London s approach, only the atomic orbitals are modified, this method is fully transparent to the treatment of the electronic structure otherwise. 

A basic defect of this type of theory is that it does not give a correct description of an isolated atom in a magnetic field. To remedy this, we follow London49 and write each molecular orbital as a linear combination of gauge-invariant atomic orbitals (GIAO) x >,... 

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