Why does the HOMO-LUMO gap calculated using ground-state DFT differ from the HOMO-LUMO gap and excitation energies obtained through TDDFT? What are the fundamental reasons for these discrepancies? Please anyone can provide the literaure that explin the theory behind it?
You already posted the same question two weeks ago:
https://www.researchgate.net/post/Why_does_the_HOMO-LUMO_gap_calculated_using_ground-state_DFT_differ_from_the_HOMO-LUMO_gap_and_excitation_energies_obtained_through_TDDFT
What additional question do you have?
Jürgen Weippert, Are there any books or literature that explain the difference between ground-state DFT-based HOMO-LUMO levels/gap and TDDFT-derived excitation energies or optical gaps? I am looking for references about it.
As a rule of thumb one is normally more focused on the tendencies of the energies calculated in DFT rather than the absolute value of each energy. Hartree-Fock, DFT and TD-DFT will all give different energetic values, depending also on the basis set used and the functional used (in the case of DFT). What would represent a good calculation framework would be the one whoe HOMO/LUMO values correctly follow the experimental trends known (something that not necessarily always happens).
Beenish Ajmal
The point is that there is no mathematical reason why these energies should be the same. However, if you want detailed books, here are two:
Book A Primer in Density Functional Theory
Book Fundamentals of Time-Dependent Density Functional Theory
The HOMO and LUMO are orthogonal, but S0 and S1 are not.
The H-L transition is just one of the main configurations of S0-S1.
So the H-L gap does not coincide with the excitation energy.
For direct transitions in inorganic periodic systems, the H-L gap and excitation energies will likely be similar, but this is only useful for understanding trends.
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts