Homogeneity under density scaling and calculating negative electron
affinities
Alex Borgoo
Durham University, Angleterre
Mercredi 7 mars à 14h, bibliothèque LCT, tour 12-13, 4e étage
The homogeneity under density scaling of the exchange-correlation and
non-interacting kinetic energy functionals of Kohn-Sham density functional
theory is investigated. Paying attention to the integer discontinuity,
results for atoms and small molecules are presented. For the
exchange-correlation functional, effective homogeneities are highly
system-dependent on either side of the integer discontinuity. By contrast,
the average homogeneity associated with the potential that averages over the
discontinuity is generally close to 4/3 when the discontinuity is computed
using positive affinities for systems that do bind an excess electron and
negative affinities for those that do not. The proximity to 4/3 becomes
increasingly pronounced with increasing atomic number. Evaluating the
discontinuity using a zero affinity in systems that do not bind an excess
electron instead leads to effective homogeneities on the electron abundant
side that are close to 4/3. For the non-interacting kinetic energy
functional, the effective homogeneities are less system-dependent and the
effect of the integer discontinuity is less pronounced. Average values are
uniformly below 5/3.
The evaluation of a previously developed expression for negative electron
affinities in Kohn-Sham density functional theory is revisited. Exploring the
implications of the homogeneity properties of the PBE exchange-correlation
functional, the orbital energies are shifted to improve estimated electron
affinities and an optimal homogeneity is established.
[1] Effective homogeneity of the exchange-correlation and non-interacting
kinetic energy functionals under density scaling
A. Borgoo, A.M. Teale, and D.J. Tozer, J. Chem. Phys. 136 (2012) 034101.
[2] Homogeneity considerations to improve negative affinity estimates
A. Borgoo, D.J. Tozer, in preparation