The DFT/CIS approach proves beneficial because the Kohn-Sham eigenvalue gaps ε KS a -ε KS i are approximations to excitation energies in a way that their Hartree-Fock counterparts (which are typically much larger) are not. This leads to less configuration mixing in the excited state. In part, this is due to the fact that Kohn-Sham calculations often result in one or more bound virtual orbitals (ε a < 0), even when approximate XC functionals are used, whereas the Hartree-Fock virtual orbitals are often all unbound, therefore significant configuration mixing is required in order to obtain localized excited states from discretized continuum orbitals. Unlike the working equations for linear-response TD-DFT, 10 the matrix elements in Eq. ( ) do not contain an XC kernel but are instead CIS-like, albeit with empirical parameters added to the diagonal matrix elements in Eq. (3a). These include a scaling-down of the exchange integral, for which Grimme uses the value c 1 = 0.317. This parameter compensates for semilocal DFT exchange that is included in the SCF calculation that is used to obtain the MOs. A shift is also added to the diagonal elements, of the form 9