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Re: [lammps-users] Need help with understanding the run start/stop implement
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Re: [lammps-users] Need help with understanding the run start/stop implement

From: Steve Plimpton <sjplimp@...24...>
Date: Tue, 17 Apr 2018 08:40:51 -0600

I assume what you are trying to do is ramp the temp from T1 to T2
smoothly over several runs.

First try doing it w/out the loop.  Just use several successive run commands
and specify the same start T1 and stop T2 values in each and
see what the temp does.

They you should be able to understand how to embed the same series
of run commands in a loop.


On Fri, Apr 13, 2018 at 10:15 AM, Chilakalapudi, Syamal Praneeth (INT) <syamal.chilakalapudi@...1550...> wrote:

Hi all,

I am trying to ramp temperature in multiple runs using the run start/stop command, like mentioned here and here.
I currently use the 5Feb18 version of LAMMPS. To give you a rough idea of what I am doing:

<initalisation, thermo, minimize>
reset_timestep 0

fix             f1 all nve
fix             f2 all temp/berendsen 3000 400 0.1

label l1
variable a loop 2
fix     deposit <some atoms at some rate>
run     20000 start $(step) stop 40000
#instead of run 20000
next    a
jump l1

There is definitely a difference between using two separate runs, and using the run start/stop command.
However, what I am unable to see is a uniform ramping over the entire 40000 time steps.

I have attached T vs time plots relevant to this discussion:

  1. Img1: Run 40000 steps with no break (and this is how I want the subsequent runs to resemble).
  2. Img2: Run 40000 steps. Using run start/stop, make 2 runs of 20000 steps each.
  3. Img3: Two separate runs of 20000 steps. Total steps still remains at 40000.

Is this the expected behavior? If yes, what must I do to make multiple runs which still resemble a single run?

Thanks a lot for your time.



Karlsruhe Institute of Technology (KIT),
Institute of Nanotechnology (INT)
M.Sc. Phys. Syamal Praneeth Chilakalapudi
Building 640, Campus North,
Hermann-von-Helmholtz-Platz 1,
76344 Eggenstein-Leopoldshafen, Germany

Phone: +49 721 608-28115

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