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

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Accurate computation of electronic absorption and circular dichroism spectra is crucial for understanding molecular properties.
• Traditional methods like time-dependent density functional theory (TD-DFT) can be computationally expensive for large molecular systems.

Purpose of the Study:

• To develop and present an efficient exciton coupling (ExC) approach based on simplified TD-DFT (sTD-DFT).
• To enable rapid calculation of excitation spectra for large molecular aggregates and soft matter.
• To investigate the role of electrostatic embedding and simplify it using a dielectric continuum.

Main Methods:

• Developed an exciton coupling (ExC) Hamiltonian from a parent sTD-DFT method, assuming nonoverlapping fragments and neglecting interfragment charge transfer.
• Implemented the approach for Tamm-Dancoff-approximated and random-phase-approximation eigenvalue problems.
• Investigated electrostatic embedding using a dielectric continuum to reduce computational complexity.

Main Results:

• The ExC approach achieves computational speedups of approximately two orders of magnitude compared to sTD-DFT.
• Calculations for systems up to ~10,000 atoms can be performed in minutes.
• The ExC-sTD-DFT method reproduces electronic absorption and circular dichroism spectra comparable to the parent sTD-DFT for separated fragments.

Conclusions:

• The ExC-sTD-DFT method offers a highly efficient and broadly applicable tool for calculating spectral properties of molecular aggregates.
• This method facilitates the screening of photophysical properties in large molecular systems and soft matter.
• The use of a dielectric continuum for embedding further enhances computational efficiency.