To use the XP-PCM model in Gaussian, you should include the N keyword in the input file, along with the other keywords that are used to specify the PCM model.

The basic syntax for the PCM model in Gaussian is as follows:

#P PCM(Solvent=model) IOp(3/33=1,3/76=value) N=value

Where model is the name of the solvent (e.g., water, methanol, etc.) and value is the exponent of the Pauli repulsion term.

For example, if you want to use the XP-PCM model with water as the solvent and N = 0.5, your input file would look like this:

#P PCM(Solvent=Water) IOp(3/33=1,3/76=13) N=0.5

It's worth noting that the optimal value of N may depend on the specific system you are studying and the level of theory you are using, so it may be necessary to conduct a series of calculations to find the optimal value of N.

It's also worth mentioning that Gaussian also offers the implementation of other models like COSMO-RS, COSMO-SAC, etc. that can be used to calculate the solvation free energy.

Thank you so much sir for answer

Sir i have find error by appling N keyword in my gaussian input file