We present a gauge-origin independent formulation of the Faraday B term of magnetic circular dichroism and of the Verdet constant of magneto-optical rotation, in terms of first derivatives with respect to the magnetic field strength of gauge invariant coupled cluster response functionals [1]. Gauge invariance is ensured by the derivative formulation in connection with the use of a magnetic field dependent basis of atomic orbitals, the so-called London orbitals. To our knowledge this represent the first application of London atomic orbitals to the calculation of frequency dependent quadratic response properties. The approach can easily be extended to other wavefunction models, and to any other frequency dependent property which can be formulated as total derivative of a (frequency-dependent) functional with respect to the field strengths of a static magnetic perturbation. In other words, any properties for which the frequency dependence is not associated with the magnetic field. This is for example the case for the hypermagnetizabilities in the Cotton-Moutton effect. The implementation of the derived equations is currently undertaken for a CCSD wavefunction on a local version of the Dalton program.
[1] S. Coriani, C. H\ue4ttig, P. J\uf8rgensen, T. Helgake
