MIL-53(Cr) flexible MOF MD problem

[merdan]

Hi everyone, I have a problem with MD simulation of water diffusion in MIL-53(Cr) flexible MOF. I want to reproduce some simulation results that i read in the some article.  In the article, it is mentioned that diffusion of 5 water molecule (Tip4p2005 model) per unit cell of MIL-53(Cr) flexible MOF will decrease volume of MOF from 1480 A^3 to around 1050 A^3. Simulation conditions are given in the article as follows,

simulation type MD
ensemble NPT
temperature 300K
timestep 0.001
total time 2ns

I used forcefield mixing rules and forcefield definition files which i found in the raspa examples files for MIL-53Cr MOF. But after simulation finished, there is no observable reduction in volume, it changed very little around initial volume 1480 A^3. I don't know what is the problem, i will share my input files. Can you give some idea? thanks.

link for files : https://drive.google.com/open?id=1hsrNft_pGlJzLnRTQcEGRceDNCYNLBtC

[David Dubbeldam]

I would do this as a function of loading. Around 2 waters per unit cell many models start to collapse (the same for CO2).
So five water molecule might be so high that the unit cell starts to become larger again.