An Efficient Exciton Coupling Scheme Based on Simplified Time-Dependent Density Functional Theory

Journal of Chemical Theory and Computation, vol. 21, pp. 7002–7016

Abstract

A very efficient and broadly applicable exciton coupling (ExC) approach based on simplified time-dependent density functional theory (sTD-DFT) is presented. Starting from this parent method, nonoverlapping fragments and neglect of interfragment charge transfer excitations are assumed to arrive at the ExC procedure. This leads to an ExC Hamiltonian that provides equivalent electronic absorption and circular dichroism spectra as the parent sTD-DFT method for largely separated fragments. The ExC approach easily accelerates the computation of such spectra of molecular aggregates by about 2 orders of magnitude compared to sTD-DFT. The latter itself is already faster by about 4-5 orders of magnitude compared to regular TD-DFT. We demonstrate the performance of the approach for excitation spectra of organic molecular clusters. Given that the fragment electronic structure in the ExC-sTD-DFT approach is solved independently, computation of spectra for systems with ∼10,000 atoms can be performed within minutes of computation time. Furthermore, the role of electrostatic embedding in the independent fragments is investigated. For the purposes covered in this work, the embedding can be simplified by employing a dielectric continuum, thus greatly reducing the overall computational complexity. This approach may be used in screening photophysical properties of large molecular aggregates and soft matter materials. We present the derivation and implementation for the Tamm-Dancoff-approximated and the random-phase-approximation eigenvalue problems. Benchmarks compared to the parent sTD-DFT methods are shown for absorption and electronic circular dichroism spectra.

Authors 4

1. Mike Pauls Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, Melatener Str. 20, 52056 Aachen, Germany

2. Jan Kubelka

   University of Wyoming

   Affiliation as printed

   Center of Innovation for Flow through Porous Media, Department of Petroleum Engineering

   University of Wyoming

3. Francesca Plückhahn Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, Melatener Str. 20, 52056 Aachen, Germany

4. Christoph Bannwarth corresponding Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, Melatener Str. 20, 52056 Aachen, Germany