Another issue need to be corrected on this page.
" Method 2: Umbrella sampling"
" LAMMPS input script
If you are using LAMMPS–GUI, open the file named free-energy.lmp. Alternatively, if you are not using LAMMPS–GUI, create a new input file and paste in the following content."
Based on the context below, I think the “free-energy.lmp” here should be " umbrella-sampling.lmp"