Description of ground and excited electronic states by ensemble density functional method with extended active space

Michael Filatov; Todd J Martínez; Kwang S Kim

doi:10.1063/1.4996873

Description of ground and excited electronic states by ensemble density functional method with extended active space

J Chem Phys. 2017 Aug 14;147(6):064104. doi: 10.1063/1.4996873.

Authors

Michael Filatov¹, Todd J Martínez², Kwang S Kim¹

Affiliations

¹ Department of Chemistry, School of Natural Sciences, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, South Korea.
² Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.

PMID: 28810777
DOI: 10.1063/1.4996873

Abstract

An extended variant of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, the REKS(4,4) method, designed to describe the ground electronic states of strongly multireference systems is modified to enable calculation of excited states within the time-independent variational formalism. The new method, the state-interaction state-averaged REKS(4,4), i.e., SI-SA-REKS(4,4), is capable of describing several excited states of a molecule involving double bond cleavage, polyradical character, or multiple chromophoric units. We demonstrate that the new method correctly describes the ground and the lowest singlet excited states of a molecule (ethylene) undergoing double bond cleavage. The applicability of the new method for excitonic states is illustrated with π stacked ethylene and tetracene dimers. We conclude that the new method can describe a wide range of multireference phenomena.