With the recursive program developed by our group,47 it is possible to evaluate eqn (23) for any response property, including the calculation of the required perturbed Fock and density matrices, as long as external routines are available that can provide the necessary (un)perturbed one- and two-electron integral contributions,56–58 exchange–correlation contributions59,60 and perturbed nuclear potential contributions, and solve the response equations61,62 that arise during the evaluation of perturbed Fock and density matrices. More information about the external modules used in this work is given in Section 3. All such modules used in the present work have been parallelized; see e.g. ref. 63.