I am optimizing complexes and used the following as parameters #P B3LYP/6-31G* Opt Freq Pop=(Regular,NBORead) Density=Current. How I can find HOMO LUMOs in .log file from Gaussian?
This is easy. You can find in the output file something like this
**********************************************************************
Population analysis using the SCF Density.
**********************************************************************
Alpha occ. eigenvalues -- -20.55498 -1.34387 -0.70920 -0.57622 -0.50409
Alpha virt. eigenvalues -- 0.14207 0.20370 0.54392 0.59886 0.66909
The last occ. eigenvalues -0.50409 a.u. is the HOMO energy. The first virt. eigenvalues 0.14207 a.u. is the LUMO energy. If you are performing a restricted closed-shell DFT calculation, this is what you want.
If you are performing an unrestricted DFT (UDFT) calculation, what I show is alpha HOMO, alpha LUMO. There would be corresponding beta HOMO, beta LUMO, which you can find after the Alpha eigenvalues section.
Jingxiang Zou Thank You!
Yes, I am performing UDFT. Among alpha and beta which one could be used for HOMO and LUMO calculations.
The idea to find/determine HOMO, LUMO for any system is dangerous/brutal. There is no math or physical theorem which says that there exists a HOMO and LUMO for any system. And HOMO, LUMO is not well-defined for all systems and all theoretical methods.
In the UDFT case, they are just alpha HOMO, alpha LUMO, beta HOMO, beta LUMO. You can tell other people the alpha HOMO-LUMO gap, and/or the beta HOMO-LUMO gap. But do not say something like this "this is HOMO, that is LUMO". My suggestion is better not to create a concept/quantity which does not exist in such case.
This qusetion you can refer to https://www.researchgate.net/post/What_are_the_alpha_orbitals_and_beta_orbitals_and_their_importance_in_DFT_calculations?isAnswerFieldFocused=true
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