A model hamiltonian tuned toward high level ab initio calculations to describe the character of excitonic states in perylenebisimide aggregates

Wenlan Liu; Sofia Canola; Andreas Köhn; Bernd Engels; Fabrizia Negri; Reinhold F Fink

doi:10.1002/jcc.25374

A model hamiltonian tuned toward high level ab initio calculations to describe the character of excitonic states in perylenebisimide aggregates

J Comput Chem. 2018 Sep 15;39(24):1979-1989. doi: 10.1002/jcc.25374.

Authors

Wenlan Liu^{1

2

3}, Sofia Canola^{3

4}, Andreas Köhn², Bernd Engels⁵, Fabrizia Negri⁴, Reinhold F Fink³

Affiliations

¹ Chongqing Key Laboratory of Green Synthesis and Applications & College of Chemistry, Chongqing Normal University, Chongqing 401331, China.
² Institute of Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
³ Institute of Physical and Theoretical Chemistry, Auf der Morgenstelle 18, University of Tübingen, 72076 Tübingen, Germany.
⁴ Universitá di Bologna Dipartimento di Chimica 'G. Ciamician', Via F. Selmi 2, Bologna 40126, Italy.
⁵ Institute of Physical and Theoretical Chemistry, Emil-Fischer-Str. 42, University of Würzburg, 97074 Würzburg, Germany.

PMID: 30315587
DOI: 10.1002/jcc.25374

Abstract

On the example of an aggregate of two perylenebisimide (PBI) molecules the character of the lowest excited electronic states in terms of charge transfer (CT) and Frenkel exciton (FE) configurations is investigated as a function of the intermolecular arrangement. A minimal model Hamiltonian based on two FE and two CT configurations at the frontier-orbitals CIS (FOCIS) level is shown to represent a simple and comprehensible approach providing insight into the physical significance of the model Hamiltonian matrix elements. The recently introduced analysis and diabatization procedure (Liu et al., J. Chem. Phys. 2015, 143, 084106 ) method is used to extract the energies of the configurations and their interactions (the model Hamiltonian parameters) also from the accurate CC2 approach. An analysis in terms of diabatic energy profiles and their interactions shows that the FOCIS parameters give a qualitatively correct description of the adiabatic excited state energy profiles. Comparison with CC2 reveals, however, the presence of avoided crossings at FOCIS level, associated with a large character change (CT/FE) of the excited states as a function of the aggregate structure, which represents the major drawback of FOCIS results. We show that proper amendment of the FOCIS-derived parameters allows to accurately represent the potential energy surfaces and crossings of the excited dimer states as a function of the aggregate structure. © 2018 Wiley Periodicals, Inc.

Keywords: Frenkel excitonic state; aggregates; charge transfer state; model Hamiltonian; perylenebisimide.

Abstract

Grants and funding