title: Orbitals from local RDMFT: Are they Kohn-Sham or natural orbitals?
abstract: Recently, an approximate theoretical framework was introduced, called local reduced density matrix functional theory (local-RDMFT), where functionals of the one-body reduced density matrix (1-RDM) are minimized under the additional condition that the optimal orbitals satisfy a single electron Schrödinger equation with a local potential. In the present work, we focus on the character of these optimal orbitals. In particular, we compare orbitals obtained by local-RDMFT with those obtained with the full minimization (without the extra condition) by contrasting them against the exact NOs and orbitals from a density functional calculation using the local density approximation (LDA). We find that the orbitals from local-RMDFT are very close to LDA orbitals, contrary to those of the full minimization that resemble the exact NOs. Since local RDMFT preserves the good quality of the description of strong static correlation, this finding opens the way to a mixed density/density matrix scheme, where Kohn-Sham orbitals obtain fractional occupations from a minimization of the occupation numbers using 1-RDM functionals. This will allow for a description of strong correlation at a cost only minimally higher than a density functional calculation.
authors.affiliation: Peter-Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Iris
authors.initials: I
authors.lastname: Theophilou
authors.affiliation: Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Vass. Constantinou 48, GR-11635 Athens, Greece.
authors.forename: Nektarios N
authors.initials: NN
authors.lastname: Lathiotakis
authors.affiliation: Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Nikitas I
authors.initials: NI
authors.lastname: Gidopoulos
authors.affiliation: Max Planck Institute for the Structure and Dynamics of Matter and Center for Free-Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany.
authors.forename: Angel
authors.initials: A
authors.lastname: Rubio
authors.affiliation: Peter-Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Helbig