, where ε ∞ is the optical dielectric constant. Then, during the calculation for the final state, the electrostatic potential on each tessera V final is computed in the presence of the fixed Q slow init . The fast component of the ASC at the final state Q fast final is obtained by solving Eq. ( ) using V final and ε ∞ instead of ε. The density used for obtaining Q slow init and Q fast final can be determined at either the SCF or PT2 level. The SCF density is directly obtained as a result of solving the SCF equation, while the PT2 density must be found iteratively by solving the SCF and PT2 equations, as done in the PTED approach. Since using the PT2 density is impractical, the SCF density is used for computing non-equilibrium energies as well.