Hey there,
As a synthetic chemist delving into theoretical calculations for my imidazolium-based organic molecules, I would greatly appreciate any guidance on the appropriate input instructions and basis sets to use for calculating the HOMO and LUMO. If possible, it would be incredibly helpful to receive links to papers or DOI numbers for further reference. Thank you very much for your valuable advice.
Regards,
Ilavarasan V
Project Fellow
Jain university
Your question is incorrectly posed since HOMO and LUMO, as well as all occupied and some virtual orbitals, will be obtained as a result of any quantum chemical calculation.
Thank you for your response.
I am completely new to theoretical studies; I am exploring this field by myself. Let me use this response to rephrase the question.
What basis set and input instructions should I use in ORCA to perform a DFT calculation on imidazolium-based organic salts, to get accurate results?
In my opinion, PBE0/Def2-TZVP is the best choice.
! RKS PBE0 def2-TZVP autoAUX RIJCOSX OPT
But then the question remains: what exactly do you need - orbital energies, shape, composition? It all depends on what analysis you will use. By default, Mulliken analysis is used. What is better depends on your specific task.
Thank you for the valuable information. The molecules I have synthesized exhibit fluorescence, and I'm keen to explore the energy gap between the ground state and the excited state through theoretical calculations.
Your insights are greatly appreciated.
I think the problem is that you need to calculate not the difference between HOMO and LUMO, but the difference between HOMO and HOMO in the singlet and triplet state.
As far as my understanding, I have to find out the energy gap between singlet excited state and singlet ground state, as, this energy gap is typically close to the energy gap between HOMO and LUMO, in case of fluorescent molecules. On the other hand, the energy gap is between triplet and singlet ground state is explored for molecules exhibiting phosphorescence.
Instead of reading the clever ones, I think you should have a look at the following link:
https://www.researchgate.net/post/which_is_best_functional_for_homo-lumo_gap_calculation_of_organic_molecules
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