This title appears in the Scientific Report : 2016 

Conditions for Describing Triplet States in Reduced Density Matrix Functional Theory
Theophilou, Iris (Corresponding author)
Lathiotakis, Nektarios N. / Helbig, Nicole
Quanten-Theorie der Materialien; IAS-1
Quanten-Theorie der Materialien; PGI-1
Journal of chemical theory and computation, 12 (2016) 6, S. 2668 - 2678
Washington, DC American Chemical Society (ACS) 2016
Journal Article
Ab initio description of double and charge transfer excitations
Controlling Configuration-Based Phenomena
Controlling Spin-Based Phenomena
Please use the identifier: in citations.
Please use the identifier: in citations.
We consider necessary conditions for the one-body reduced density matrix (1RDM) to correspond to a triplet wave function of a two-electron system. The conditions concern the occupation numbers and are different for the high spin projections, Sz = ±1, and the Sz = 0 projection. Hence, they can be used to test if an approximate 1RDM functional yields the same energies for both projections. We employ these conditions in reduced density matrix functional theory calculations for the triplet excitations of two-electron systems. In addition, we propose that these conditions can be used in the calculation of triplet states of systems with more than two electrons by restricting the active space. We assess this procedure in calculations for a few atomic and molecular systems. We show that the quality of the optimal 1RDMs improves by applying the conditions in all the cases we studied.