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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 08:59:52 -0600

yes, this is correct, same start and stop in each run.
Not start T1 and stop T2 as I wrote earlier.  Good catch.

Steve


On Tue, Apr 17, 2018 at 8:51 AM, Pengyu Huang <hughh.py@...24...> wrote:
I have kept forgetting to reply to LAMMPS Users Mailing list... I think the problem should be solved by using a start time of 0 instead of $(step). I am posting my previous reply again:

Hi Syamal, 

Just had a quick look at the document for run:

For example, consider this fix followed by 10 run commands:

fix         1 all nvt 200.0 300.0 1.0
run         1000 start 0 stop 10000
run         1000 start 0 stop 10000
...
run         1000 start 0 stop 10000

The NVT fix ramps the target temperature from 200.0 to 300.0 during a run. If the run commands did not have the start/stop keywords (just “run 1000”), then the temperature would ramp from 200.0 to 300.0 during the 1000 steps of each run. With the start/stop keywords, the ramping takes place over the 10000 steps of all runs together.


This explains why you did not get something you expected, as you have changed your start time.

Regards,
Pengyu



On Wed, Apr 18, 2018 at 12:40 AM, Steve Plimpton <sjplimp@...24...> wrote:
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.

Steve

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    run.in 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.

Regards,

Praneeth

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

Phone: +49 721 608-28115
Web: https://www.int.kit.edu/clustermaterials.php
        https://www.int.kit.edu/nanosim

KIT---the research university in the Helmholtz Association


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