From you experience, which DFT method and basis sets are recommended for organic molecules optimization using Gaussian and provide a trusted energy and proprieties ( e.g UV-vis spectra)
Before running into geometry optimizations of small organic molecules search at PubMed site: https://pubchem.ncbi.nlm.nih.gov/
Absorption of UV-VIS spectra at the DFT level you have to "dive" into TD-DFT methods, https://gaussian.com/td/
I am NOT an expert on that...
As for your question on basis-set you always start with a medium basis set, on a optimized geometry in order to get used to the results log file.
Article UV/Visible spectra of natural polyphenols: A time-dependent ...
B3P86/6-311+G(d,p) means Becke-functionalto calculate correlation plus PerdewWang-1986 to calculate exchange.
The basis-set is Pople type (very good basis) 6-311 gaussians plus d and p polarization‐basis.
Write me in case you encounter problems with the PubChem optimized geometry. In the Gaussian Support page you'll find basis-set details:
https://gaussian.com/basissets/
For full optimization with B3LYP, I recommend to use 6-311G basis set. In ascorbic acid you won't need polarization functions. This is a previous step.
Once you get a "stable geometry" you may proceed to a newer basis-set, lets say cc-pVTZ which gives you a quicker and more accurate solution than 6-311+G(d,p). cc-pTZV are consistent for correlation.
Hello Manal Alwahsh
Choosing methods and basis for organic molecules depends upon the nature of the problem one is studying. You may find that for the DFT, basis set dependency is less for a particular functional. But if one is targeting the excited state ( may or may not use solvent), Then the choice of DFT functional becomes quite essential. Review articles are available where benchmarks are performed for various types of molecules for different excited properties; in your case, it could be the absorption spectrum.
- Badges
- Science topic