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Re: The best dft method for TDDFT of C=O containing compounds


Dear Alisher,

can you show your molecule? In some cases, band assignment made by experimentalists is simply incorrect. In other cases, it is TDDFT that misplaces the transitions of different nature (n-pi, pi-pi*, or charge-transfer). You can look at the effect of HF exchange in the functional by using the following series: BLYP (0% HF exchange) - B3LYP (20%) - BHHLYP (50%) - LYP (100%). If the effect is strong, CASSCF-XMCQDPT can be the method of choice. An alternative way is to use range-separated hybrid functionals, such as LC-BLYP or CAM-B3LYP (implemented in GAMESS-US), although the results can still be questionable.

On Sun Mar 30 '14 3:36pm, Alisher wrote
>Dear Alex and Firefly users,
>I computed UV/Vis spectra of C=O containing aromatic compounds by TDDFT (B3LYP1). But, I canít found agreement between experiment and TDDFT. In the experiment, usually, n-pi* transition of the C=O group observed in the longest wavelength region then pi-pi* transition. Besides, n-pi and pi-pi* transitions also observed pi-pi* transition caused by charge transfer from aromatic fragment to the C=O group.
>Who can help me to choice the best DFT method for modeling UV/Vis?
>Thanks in advance!

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