Great that you released your gcmc-code. I am currently testing it and receive error messages like “bond atoms missing” after a few MC steps. The used data file should be fine, at least it run without problems with my gcmc code. The data file describes a silica particle (molid=1) in the middle of the box where water (molid= 2,…,1539) can adsorb on its surface. Either there is something wrong in my in.gcmc file (I selected molid=2 as template) or the code messes up something with the molids. I do not know what is the problem here, but I for instance, at the beginning had the problem that molids were duplicated (more than one molecule with the same molid), what caused problems when I tried to delete such a molecule. I attached the data and in.gcmc in an email to your address that you could test it if you want.