I would like to determine whether the following chemical reaction is spontaneous by calculating Gibbs free energy.

However, when performing the frequency property calculation in DMol3, I cannot obtain the free energy value for single atoms.

In this case, how can I calculate the Gibbs free energy for Cs+ or Li+?

Would it be acceptable to perform a frequency calculation for the solid structure of Cs or Li, and then use the value divided by the number of atoms in the cell?