Re: NVE simulations in NAMD - the right choice of timesteps and parameters

From: Axel Kohlmeyer (akohlmey_at_gmail.com)
Date: Tue Nov 29 2016 - 10:16:11 CST

On Tue, Nov 29, 2016 at 5:54 AM, Harish Srinivasan
<harishlglk1992_at_gmail.com> wrote:
> I am trying simulate micellar systems like SDS, SDBS micelle in water. I
> equilibrated the system for 20 ns using NPT Langevin piston.
> Even after 20 ns run, the average temperature remained at 295 K for the
> system (I am still pondering why this happened), so I used rescale velocity
> (with rescalefreq 2 timesteps) for 500 ps.
>
> After this I ran a NVE simulation (meaning, i switched off all the
> thermostats and barostats) for about another 20 ns, the total energy of the
> system seemed to change about 20000 units in the span of 20 ns.
>
> I am using 1 fs timestep, with 2fs for non-bonded forces and 4fs for full
> electrostatics. No rigidity imposed.

1 fs is far too large a time step for unconstained hydrogen atoms. try
something in the range 0.25 - 0.5fs

axel.
>
> Thank you,
> Harish
>
>

-- 
Dr. Axel Kohlmeyer  akohlmey_at_gmail.com  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.

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