I am trying to optimize a basis set and a particular level of theory to reach the experimental results for UV-Visible spectrum. Can anyone suggest how to incorporate the scaling factors for Gaussian calculations?
Please help me anyone regarding this issue.
Thank you in advance.
Scale factor are used for calculated vibrational frequencies, to compensate for the harmonic approximation, finite basis sets and absent or incomplete incorporation of electron correlation in the theory.
They are important only for the calculation of vibrational frequencies or their dependent properties, like zero point energies or thermodynamic quantities.
UV-Visible spectra are related to molecular orbital energy differences.
There are two kind of linear scaling procedure we can incorporate while performing vibrational frequency calculations. i) linear scaling procedure ii) selective scaling procedure. For small molecules, linear scaling is enough to correct the calculated frequencies nearer to experimental one.
For large sized molecules, selective scaling procedure only give the better results. When we use MOLVIB program package to find the PED, we need arc file, dat file and FF file. After molvib run, scaling factor is to be modified in the program input. Then we get corrected output.
if you are trying to use MOLVIB for calculations, feel free to contact me.
by
Karthick
UV spectras can hardly be calculated reasonably with the gaussian program. Normally you use extended MR-CI or CASSCF-Perturbation (for example PT2) calculations on smaller systems. The CIS method of Gaussian may help to consider for larger systems to guess the electronic states involved, but be careful when relying only on CIS calcualtions.
There were many papers about it, one by me. You can just multiply the frequencies (GAMESS even has it as Input), or you scale the force constant and read it in again.
- Badges
- Science topic