Trabajo presentado al: "Deutsche Physikalische Gesellschaft Spring Meeting" celebrado en Dresden (Alemania) del 30 de marzo al 4 de Abril de 2014.Standard local exchange-correlation and semi-local functionals in ground-state density functional theory are known for their shortcomings in describing correct charge transfer, dissociation energies of
molecular ions, and barriers of chemical reactions.
To understand the failures of approximate functionals and to gain insight into the behavior of the exact functional, we investigate the exact solution of the many-body Schrödinger equation for a lattice
model. Using exact diagonalization, we explicitely construct the exact Hohenberg-Kohn functional and the mapping from densities to wavefunctions. Besides the normal inter-system derivative discontinuity
widely discussed in the density-functional theory community, we observe a new feature of the exact functional in the low-density
limit. This "intra-system derivative discontinuity" resembles the inter-system derivative discontinuity, but is within the system.
The description of many physical phenomena linked to charge-transfer processes (both in the static and dynamical regimes) require a proper account of this "intra-system derivative discontinuity".Peer reviewe
