I ran sorption module for methane adsorption on MOF-5 at 150 K.at 693  kPa. at the different run with same input i got 188.4,190.6, 196.5  number of methane on MOF-5 after 1000000 equilibration and same  production steps. while i ran same thing with my own GCMC code i got  200.4,200.4,200.1 in three same runs . I used UFF force-field and  methane  1site model. Please can any one suggest the reason of why at three  different run , number of adsorbed methane are differed much? Please Tell how to specifiy rigid adsorbate(Framework, guest) during the simulation?

Please reply. thanks a lok

Amar Deep