Suggestion for UV-vis and IR Calcualtion in gaussian

rpestana94

Hi, I want to calculate UV-VIS and IR spectrum for some porphyrins (as image show) using gaussian, I have doubt about the method and the basis set, I was thinking to use  
b3lyp/lanl2dz empiricaldispersion=gd3bj, but not sure, maybe using PBE can give better results.
I will change Iron for Cu, Sn and Zn.


Thanks in advance for any recomendations

sobereva

Use PBE0. Pure functionals such as PBE almost always underestimate excitation energy and should never be used.

Use 6-311G* for ligands, and SDD for transition metals. Lanl2DZ is too poor.

rpestana94

sobereva 发表于 2023-11-20 13:12
Use PBE0. Pure functionals such as PBE almost always underestimate excitation energy and should neve ...

Thanks professor, in this case the empirical dispersion should be added or for PBE0 and SDD is not necessary? I know for B3LYP we always have to use it

sobereva

rpestana94 发表于 2023-11-21 03:39
Thanks professor, in this case the empirical dispersion should be added or for PBE0 and SDD is not ...

DFT-D dispersion correction doesn't directly affect electron excitation calculations.

rpestana94

sobereva 发表于 2023-11-20 15:16
DFT-D dispersion correction doesn't directly affect electron excitation calculations.

Thanks professor

rpestana94

sobereva 发表于 2023-11-20 13:12
Use PBE0. Pure functionals such as PBE almost always underestimate excitation energy and should neve ...

Professor in case of considering a solvent, which is the best option IEFPCM, SMD or CPCM? For UV and IR calculation.
Also the solvent should be considered in the optimization and the UV calculation or just in the UV?

And last, do you have some recommendation to read about this methods, I always get confused, thanks in advance.

sobereva

rpestana94 发表于 2023-11-24 23:55
Professor in case of considering a solvent, which is the best option IEFPCM, SMD or CPCM? For UV a ...

Without special reason, always use IEFPCM, which is also the default choice when using "scrf" keyword. Only when you need to calculate quantities related to energies, SMD usually perform better since it explicitly considers non-polar contribution of solvation effect. CPCM should never be used for Gaussian users, unless you hope to exactly reproduce data in literatures in which CPCM was employed.