There are a lot of complicating factors in your example. Also, it is gigantic. I can’t check every possible thing you might be doing wrong. However, I did run my own tests on a modified version of in.gcmc.lj, in which I ran two gcmc fixes with two LAMMPS types with identical interaction coefficients. The total density and pressure of the system came out slightly lower than for the 1-component case, while the excess chemical potential came out slightly higher. I think is due to the fact the ideal gas contribution to chemical potential is different by shifted by kTln(2) for 2-component case. In any event, the numbers of types 1 and 2 are the same, within statistical noise.
in.gcmc.lj2 (2.35 KB)