Open AccessDescription of ground and excited electronic states by ensemble density functional method with extended active space
Author(s) -
Michael Filatov,
Todd J. Martı́nez,
Kwang S. Kim
Publication year - 2017
Publication title -
journal of chemical physics online/the journal of chemical physics/journal of chemical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.071
H-Index - 357
eISSN - 1089-7690
pISSN - 0021-9606
DOI - 10.1063/1.4996873
Subject(s) - excited state , complete active space , singlet state , excited electronic state , tetracene , ground state , formalism (music) , chemistry , molecule , multireference configuration interaction , singlet fission , atomic physics , density functional theory , computational chemistry , quantum mechanics , configuration interaction , physics , art , musical , basis set , visual arts
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