This polarization has been called distortion energy, or induction energy, and is defined as the difference between E sol QM and the in vacuo counterpart, E vac QM . In this work, we employ a straightforward approximation of the distortion energy (noted as E D QM ) based on its intrinsic relation with the polarization correction, proposing a linear relation with the polarization energy, with a positive proportionality constant k to be determined: