Since our main focus is to have a better understanding of the relationship between polarizability and HOMO-LUMO gap in organic molecules, we first revisit different qualitative and quantitative models employed to compute them. Typically, accurate electronic structure methods, such as coupled cluster or hybrid DFT are used to determine these properties . Practically, any mean-field electronic structure method allows to calculate a HOMO-LUMO gap, but the results are sensitive to the method chosen . Moreover, since the Kohn-Sham gap is not an experimental quantity, the ambiguity regarding the accuracy of different methods is not trivial to resolve. Polarizability (α) is typically obtained from finite field, coupled perturbed Hartree-Fock or density functional perturbation theory (DFPT) calculations . However, these electronic structure methods need considerable computational resources when dealing with larger molecules or significant swaths of the CCS. Accordingly, we will next discuss alternative physical models, empirical correlations as well as approximate methods to obtain these QM properties. We will start with examining the polarizability, for which analytical models (such as the quantum Drude oscillator, or QDO) as well as empirical correlations and predictive semiempirical methods are available. After this, the models for HOMO-LUMO gap will be mentioned, before concluding the section by analyzing what is known about the correlation between these two quantities.