Dear Bijan Kumar Paul

To incorporate a dispersion-corrected counterpart of B3LYP in Gaussian09, you can use the B3LYP-D or B3LYP-D3 functionals, which add empirical dispersion corrections to the standard B3LYP functional. Gaussian09 supports the Grimme dispersion corrections (e.g., D2 or D3), which you can activate by including appropriate keywords in your input file. For instance, adding the keyword EmpiricalDispersion=GD3 activates Grimme's D3 dispersion correction. Alternatively, for D2 corrections, use EmpiricalDispersion=GD2. Ensure that your route section looks something like this:

bashCopiar código# B3LYP EmpiricalDispersion=GD3

Moreover, you may specify advanced settings like dispersion damping parameters if needed, though these are generally automatically determined. It’s also important to verify the version of Gaussian09 you’re using, as some early versions may not fully support the D3 corrections. For a deeper level of accuracy, you might explore DFT-D3BJ, which includes Becke-Johnson damping. Ensure your basis set is adequate for capturing dispersion interactions (e.g., def2-TZVP or larger), as the quality of the dispersion correction heavily depends on the choice of basis. Finally, consult the Gaussian09 manual for syntax updates and guidance specific to your version.

I hope this helps.

Dear Prof. Márquez

Thank you very much for your time and the insightful guidance.

It will be immensely helpful for me.

Thank you very much.

Regards

-Bijan.