Free energy of insertion

Thanks I will try FEP.

The nigh modify include part is clear now.

I am performing a widom insertion technique to calculate the chemical potential.
I am trying to calculate the change in potential energy of inserting water molecules into the system (not the free energy, sorry). I thought the following commands would achieve that

group network type 1:20:1

delete_bonds all multi any

neigh_modify delay 0 every 1 check yes page 100000 one 2000 exclude group network network
thermo_style custom step pe ke etotal c_4 c_1 c_2 c_3
fix 4 all deposit 10000 0 1 342345 region 1 mol water attempt 1

I am also setting the bond angle coefficients of water molecules to be zero.

The potential energy from the thermo output gives the change in the potential energy as the water molecules are inserted ?.
Correct me if I am wrong.