I am interested in making calculations of non-radiative constants rates like internal conversion. There is a specific function on the Gaussian package that I can use for this purpose?
There are no specific functions for this purpose. This notwithstanding, an interesting paper was published in 2018 on the use of Gaussian only to calculate the rate constants of internal-conversion and intersystem-crossing transitions. Maybe this can be applied to your case.
Article First-principles method for calculating the rate constants o...