Dear Justin I confused, in your tutorial, parameters of ff for example: OPLS-AA rlist=rvdw=rcoulomb=1 but in another tutorial i saw : rlist=rcoulomb=0.9 rvdw= 1.4 or .8 www-personal.umich.edu/~amadi/fwspidr_tutor.pdf -- Sincerely Ali Alizadeh