Within this context, two fundamental quantummechanical (QM) electronic properties are the optical gap and the molecular dipole polarizability (α). Optical gap is an experimental property that measures the energy corresponding to the lowest observed optical transition. Many computational studies use the HOMO-LUMO gap ∆E HL (the difference between the energies of frontier molecular orbitals in the ground state) as a starting point in approximating experimental optical gaps. HOMO-LUMO gap is also related to chemical reactivity and excitation energies; and thus plays an important role in the prediction of optical absorption spectra, refractive indices and conductivity . For correctness of terminology, HOMO-LUMO gap obtained from density functional calculations should be referred to as Kohn-Sham (KS) gap. Although the relations between different gaps (Kohn-Sham, fundamental, and optical) are subtle and have been discussed in detail in the literature , in this manuscript we will use the KS gap as a proxy for observable experimental properties.