where ψ 0 and ψ j are the ground and jth excited state wavefunctions, respectively, µ is the electric dipole operator, m is the magnetic dipole operator, Greek indices correspond to Cartesian components, and ω j0 is the jth excitation frequency. This expression works in the non-resonant regime 1,64-66 and for wavelengths larger than the average molecular size. In practice, the tensor is evaluated using the linear response formalism (LR), because it does not require the evaluation of excited states. The linear response function, expressed with the notation ⟪X; Y ⟫ ω for two generic operators X and Y , can be evaluated using two representations of the electric dipole operator: