You are using rlist = 1.3 coulombtype = PME rcoulomb = 1.3 rvdw = 1.3 That is a very strange set up !!! In general when PME is used you don't want it real space to be that large. 1.0 seem to sufficient. for your pressure you put compressibility o.o on the z axes !! That is really what you want ? XAvier