Elimination of the asymptotic fractional dissociation problem in KohnSham densityfunctional theory using the ensemblegeneralization approach
Abstract
Many approximations within densityfunctional theory spuriously predict that a manyelectron system can dissociate into fractionally charged fragments. Here, we revisit the case of dissociated diatomic molecules, known to exhibit this problem when studied within standard approaches, including the local spindensity approximation (LSDA). By employing our recently proposed [E. Kraisler and L. Kronik, Phys. Rev. Lett. 110, 126403 (2013), 10.1103/PhysRevLett.110.126403] ensemble generalization we find that asymptotic fractional dissociation is eliminated in all systems examined, even if the underlying exchange correlation (xc) is still the LSDA. Furthermore, as a result of the ensemblegeneralization procedure, the KohnSham potential develops a spatial step between the dissociated atoms, reflecting the emergence of the derivative discontinuity in the xc energy functional. This step, predicted in the past for the exact KohnSham potential and observed in some of its more advanced approximate forms, is a desired feature that prevents any fractional charge transfer between the system's fragments. It is usually believed that simple xc approximations such as the LSDA cannot develop this step. Our findings show, however, that ensemble generalization to fractional electron densities automatically introduces the desired step even to the most simple approximate xc functionals and correctly predicts asymptotic integer dissociation.
 Publication:

Physical Review A
 Pub Date:
 March 2015
 DOI:
 10.1103/PhysRevA.91.032504
 arXiv:
 arXiv:1508.07580
 Bibcode:
 2015PhRvA..91c2504K
 Keywords:

 31.15.E;
 Densityfunctional theory;
 Physics  Chemical Physics;
 Physics  Atomic Physics
 EPrint:
 includes a supplementary material