pressure fluctuation

Dear Lammps users,

I simulated a box of 200 of ionic liquid molecules in NVT ensemble using:

pair_style lj/cut/coul/long 11

kspace_style pppm 1.0e-4
fix 2 all ave/time 100 1000 100000 c_thermo_press file pressure.txt

The pressure results are not well-fitted with experimental data. I chose 1 ns for run time, and the error percent between two following average pressures is about 10%. I wanted to know is it possible, if I increase the simulation time like to 10 ns, the error percent would decrease below 2 or 3 percent? My main problem is the pressure fluctuation because when I compare the pressure results with experimental it produces a great error, but the corresponding volume is ok!!! I mean, I have pVT data from the simulation, and when I compare them with pVT data of experiments, for same VT between exp. and sim. I have really different pressures( like 500% error percent in average); but when I compare the corresponding V for same pT of sim. and exp. the error percent is below 3%. I don’t understand, is my simulation could be validated via experimental result or not?

error percent=((P2-P1)/P1)*100

Dear Lammps users,

I simulated a box of 200 of ionic liquid molecules in NVT ensemble using:

pair_style lj/cut/coul/long 11

kspace_style pppm 1.0e-4
fix 2 all ave/time 100 1000 100000 c_thermo_press file pressure.txt

The pressure results are not well-fitted with experimental data. I chose 1 ns for run time, and the error percent between two following average pressures is about 10%. I wanted to know is it possible, if I increase the simulation time like to 10 ns, the error percent would decrease below 2 or 3 percent? My main problem is the pressure fluctuation because when I compare the pressure results with experimental it produces a great error, but the corresponding volume is ok!!! I mean, I have pVT data from the simulation, and when I compare them with pVT data of experiments, for same VT between exp. and sim. I have really different pressures( like 500% error percent in average); but when I compare the corresponding V for same pT of sim. and exp. the error percent is below 3%. I don’t understand, is my simulation could be validated via experimental result or not?

error percent=((P2-P1)/P1)*100

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I searched and it seems maybe adding some new steps would work:

fix 1 all nve/limit 0.1

run 100000
unfix 1
fix 3 all press/berendsen iso 1184 1184 100.0

run 50000
unfix 3

fix 6 all nvt temp 350 350 10.0
run 1000000

formerly, I just had:

fix 1 all nvt temp 350 350 10.0
run 1000000
looking for your advice.
thanks

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