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[lammps-users] How to reach to a desired( or properly equilibrated) pressure in NVT ensemble in LAMMPS?
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[lammps-users] How to reach to a desired( or properly equilibrated) pressure in NVT ensemble in LAMMPS?


From: geraili_hosein@...7110...
Date: Mon, 4 Sep 2017 13:37:36 +0430

 

I've been working on an ionic liquid that I was involved in simulating with Lammps, but when I started to write its paper, I found a mistake (or a neglect) that makes almost all the results useless. I would always compare the pVT simulation data with the corresponding experimental data with an error below 3% for the comparison of V of simulation and experimental (in P, T similar), and so I assumed my simulations are validated, but when a couple of weeks ago, I compared p simulation and experimental (in V, T similar), I found a very weird error of 50, sometimes 300%. Because of the pressure difference, I thought that this could be because of the NVT ensemble pressure fluctuation, and maybe it cannot reach the equilibrium( I used a big simulation time and the error percent between two following average pressure was revolving around almost 8%), so I tried to use pressure control methods, so I added the following commands:
fix 1 all nve / limit 0.01


fix 2 all box / relax iso 1184 vmax 0.001


run 100000
unfix 1
unfix 2
fix 3 all press / berendsen iso 1184 1184 100000.0


run 50000
unfix 3
the main input was as follows:(I included the new commands too),
units real
dimension 3
boundary p p p
atom_style full
pair_style lj / cut / coul / long 11
pair_modify mix geometric tail yes
kspace_style pppm 1.0e-4
read_data ionicdata.data
neighbor 2.0 bin
neigh_modify delay 2 every 1 check yes
fix 1 all nve / limit 0.01


fix 2 all box / relax iso 1184 vmax 0.001


run 100000
unfix 1
unfix 2
fix 3 all press / berendsen iso 1184 1184 100000.0


run 50000
unfix 3
fix 6 all nvt temp 350 350 10.0
run 1,000,000



I tried to include all the important parts. My first question is that, in your opinion, these additional commands will have any effect on the issue, and will they help me to get the desired and equilibrated pressure? The second question is that I still encounter errors, and I am trying to fix them, so if you have any comments about these codes or the new ones that I can use to get the desired pressure, please mention in your answer.


I would appreciate any advice.
Thank you in advance




 


Hosein Geraili Daronkola
M.Sc.Graduated of physical chemistry
Physical Chemistry,
Department of Chemistry,
Sharif University of Technology.
geraili.hsn@...24...