A Simple Effective SCF Method for Computing Optical Gaps in Organic Chromophores

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Organic Electronics

Background:

• Accurate computation of low-lying excited states is crucial for understanding photoluminescence in organic chromophores.
• Existing methods like Time-Dependent DFT (TDDFT) can be computationally intensive.

Purpose of the Study:

• To present an alternative, computationally efficient time-independent DFT scheme for calculating the lowest single-particle excitation energy, particularly for singlet excited states.
• To evaluate the accuracy and applicability of this new method across various organic molecules.

Main Methods:

• Utilizes a "virial"-theorem based model for singlet-triplet splitting.
• Requires a DFT calculation of the closed-shell ground state and a restricted open-shell triplet excited state.
• Involves a simple integral evaluation to determine vertical excitation energies.

Main Results:

• The proposed DFT scheme accurately computes vertical excitation energies for small molecules, polycyclic aromatic hydrocarbons, and organic dyes.
• Results show comparable accuracy to TDDFT.
• Functional dependency explored using B3LYP, wB97X, and CAM-B3LYP functionals for polyenes and linear acenes.

Conclusions:

• The developed time-independent DFT scheme provides a valid and useful method for determining optical gaps.
• Offers fair computational cost, making it an attractive alternative for excited state calculations.