Orbitals from local RDMFT: Are they Kohn-Sham or natural orbitals?

Journal of Chemical Physics 143, 054106 (2015)

Orbitals from local RDMFT: Are they Kohn-Sham or natural orbitals?

Iris Theophilou, Nektarios N. Lathiotakis, Nikitas I. Gidopoulos, Angel Rubio, Nicole Helbig

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.

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I.T. and N.H. acknowledge support from an Emmy-Noether grant from Deutsche Forschungsgemeinschaft. N.N.L. acknowledges support from the Greek Ministry of Education (EΣΠA program), GSRT action KPHΠIΣ, project “New multifunctional Nanostructured Materials and Devices—POLYNANO” (No. 447963). A.R. acknowledges financial support from the European Research Council Advanced Grant DYNamo (No. ERC-2010-AdG-267374), Spanish Grant (No. FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (No. IT578-13) and European Community FP7 project CRONOS (Grant No. 280879-2) and COST Actions CM1204 (XLIC) and MP1306 (EUSpec).

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