GCMC & excess chemical potential

hello LAMMPS users,

I have a question regarding the capabilities of ‘fix gcmc’. From the equations described in https://lammps.sandia.gov/doc/fix_gcmc.html, the ideal chemical potential (mu_id) can be calculated outside the simulation, but it does not mention a calculation or output that can provide the excess chemical potential (mu_ex). If I specify the pressure instead of the chemical potential in ‘fix gcmc’, is there a way for LAMMPS to output mu_ex? Thanks in advance.


-Leebyn Chong

Good question. Fix gcmc attempts to constrain the chemical potential of the system to match the requested target. However, fix gcmc does not estimate chemical potential, even though it does calculate energy changes that could be used for that purpose. All that is needed is a tally of the energy changes from all attempted insertions (the Widom method). Somebody should add that to the code.