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TT: Fachverband Tiefe Temperaturen

TT 52: Electronic-Structure Theory: New Concepts and Developments in Density Functional Theory and Beyond - V (joint session DS, HL, MA, MM, O, TT, organized by O)

TT 52.13: Vortrag

Mittwoch, 22. März 2017, 18:00–18:15, GER 38

Conditions for describing triplet states in reduced density matrix functional theory — Iris Theophilou¹, Nektarios N. Lathiotakis², and •Nicole Helbig³ — ¹Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany — ²Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Vass. Constantinou 48, GR-11635 Athens, Greece — ³Peter-Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany

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, S_z=± 1, and the S_z=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.