Assessment of Density Functional Methods for Exciton Binding Energies and Related Optoelectronic Properties

TL;DR

This study evaluates the accuracy of various density functional methods, particularly omegaB97 series, in calculating exciton binding energies and related properties for organic molecules, comparing them with high-level quantum chemistry methods.

Contribution

It provides a comprehensive assessment of modern DFT functionals for exciton-related properties, highlighting the superior performance of omegaB97 functionals.

Findings

omegaB97 functionals outperform others with a mean absolute error of 0.36 eV

DFT methods show varying accuracy for exciton binding energies

High-level CCSD methods serve as reliable benchmarks

Abstract

The exciton binding energy, the energy required to dissociate an excited electron-hole pair into free charge carriers, is one of the key factors to the optoelectronic performance of organic materials. However, it remains unclear whether modern quantum-mechanical calculations, mostly based on Kohn-Sham density functional theory (KS-DFT) and time-dependent density functional theory (TDDFT), are reliably accurate for exciton binding energies. In this study, the exciton binding energies and related optoelectronic properties (e.g., the ionization potentials, electron affinities, fundamental gaps, and optical gaps) of 121 small- to medium-sized molecules are calculated using KS-DFT and TDDFT with various density functionals. Our KS-DFT and TDDFT results are compared with those calculated using highly accurate CCSD and EOM-CCSD methods, respectively. The omegaB97, omegaB97X, and omegaB97X-D functionals are shown to generally outperform (with a mean absolute error of 0.36 eV) other functionals for the properties investigated.