Re: [lammps-users] [EXTERNAL] fix _gcmc question

Please read the documentation before writing long emails to the wrong address. This behavior is documented:

" When using fix gcmc in combination with fix rigid, deletion of the last remaining molecule is not allowed for technical reasons, and so the molecule count will never drop below 1, regardless of the specified chemical potential."


Hi Arben,

There are a lot of corner cases in fix gcmc, it is hard for us to document them all precisely. The key point is, there are known technical reasons why sometimes the last molecule will not get deleted and it is non-trivial effort to modify the code to enable N=0 in those cases. From a scientific viewpoint, this is not a significant limitation, because the regime of N=0,1 can usually be closely approximated by an equivalent non-interacting system. So we are not going to devote resources to handling it. You have two choices:

  1. Accept this limitation and work around it

  2. Go in to the code and handle it yourself.


Sorry, Aidan, that it went to the wrong person.

Perhaps someone else can help me with my question:

As Aidan pointed out, the documentation says that "When using fix gcmc in combination with fix rigid, …, molecule count will never drop below 1, …”

I’m not using fix_gcmc in combination with fix rigid.

Are there other cases where this is not allowed?

Thank you,