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Re: [lammps-users] About temperature fluctuations
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Re: [lammps-users] About temperature fluctuations

From: Giacomo Fiorin <giacomo.fiorin@...24...>
Date: Sun, 12 Nov 2017 20:02:32 -0500

If you set a thermostat, you should definitely communicate the important details about that thermostat, including the target temperature.

As for the temperature "that you actually get", it is difficult to converge to the thermodynamic ensemble for a small number of degrees of freedom, and large deviations are expected.


On Sat, Nov 11, 2017 at 11:09 AM, A. M.M <alaa.murar@...24...> wrote:
بسم الله الرحمن الرحيم

Hello LAMMPS user,

I used fix_langevin command with fix_nve to perform a BD as mentioned in LAMMPS documents, I put Tstart=Tstop=298.15 K (25 C) and damp = 482 fmsec. Also, I used a time step = 300.0 fmsec, and my system is a 24 bead-spring chain.

My simulation run well, but I noticed that the temperature fluctuates below the value that I put in the command, and when I calculate the ave/time/temp I also got around 150-160 K. what is/are the reason/s ?

I can increase the values in the command until I get a fluctuations around 298.15 K and also an ave/time/temp around this value, but now Can I say that the results of mu simulation are in ( ave/time/temp that I get ) or in what I used in the command ?

Thank you

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Giacomo Fiorin
Associate Professor of Research, Temple University, Philadelphia, PA
Contractor, National Institutes of Health, Bethesda, MD