In this way, the entire temperature dependence is contained in the spin dyadic. Similarly, considering Eq. (71) used for describing PCS, which is linear in the electronic magnetic moment operator, we only need the quantities ⟨⟨M el i M el j ⟩⟩ (apart from a prefactor the susceptibility tensor) and ⟨⟨M el i M el j M el k M el l ⟩⟩ (apart from a prefactor the second hypersusceptibility tensor) to obtain the three needed tensors. These quantities [spin dyadic/tetradic and (hyper)susceptibilities] are computationally simpler to evaluate than directly calculating the σ or τ tensors: since they only involve the components of a single vector operator, they are (super)symmetric (invariant under all permutations of their indices).