Activates the gradient-regulated asymptotic correction (GRAC) approach for
exchange-correlation potentials of Grüning et al.
(J. Chem. Phys. 114, 652 (2001)). The user has to supply a shift
) for the bulk potential which should
approximate the difference between the HOMO energy
) obtained from the respective standard Kohn-Sham
calculation and the (negative) ionisation potential of the
In case of gradient or laplacian functionals the modified GRAC scheme of Bast et al. (Chem. Phys. Chem. 9, 445 (2008)) is used.
If shift is set to zero in the input the program will estimate the ionisation energy from the HOMO energy during the SCF (as soon as the HOMO energy is converged to a given threshold) and then sets the bulk shift automatically. This is done by using a linear fit of DFT HOMO energies to ionisation energies calculated with the SCF method for a range of molecules (see also S. Hirata et al., J. Phys. Chem. A, 107, 10154 (2003)).