How to calculate exciton binding energy using TDDFT?

Questions
#1

Does Qchem support to calculate exciton binding energies with TDDFT .out files?

#2

The exciton binding energy is the difference between the fundamental gap (IE - EA) and the optical gap (lowest excitation energy, e.g., from TDDFT). You would need to compute the IE and the EA separately. See this paper for some definitions and some benchmarking:

#3

Thank you for the information.

#4

A different way in which you could think about exciton binding energies is that, within an individual computation, you look at the difference between the excitation energy and the weighted orbital energy gap.

We looked at that here
http://dx.doi.org/10.1021/acs.jctc.3c00125

There are three terms that contribute to the excitation energies beyond MO energies

  • Coulomb binding (termed K2)
  • Exchange repulsion (termed J2)
  • Additional XC effects (termed XC2)

You can analyse their individual contributions to the exciton binding.

This is activated with the keyword
EXCIT_ENERGY_COMPONENTS true
https://manual.q-chem.com/latest/Ch10.S2.SS10.html

#5

Thank you for the information