[CP2K-user] [CP2K:21500] Re: System exploded in NPT-F simulations

[Marcella Iannuzzi]

Dear Zhuoran

Have you also monitored the CELL , the STRESS and the energy and 
temperature of the barostat?
When they change too fast, it is difficult for the dynamics to recover. 
In this case you can try to rescale the temperature of the barostat and 
reduce the time step.
Regards
Marcella

On Saturday, May 24, 2025 at 10:38:05 AM UTC+2 zlo... at umd.edu wrote:

> Dear all,
>
> I am testing NPT simulations on the tutorial water system 
> <https://www.cp2k.org/exercises:2018_ethz_mmm:h2o_md>. I'm including the 
> following changes to the input file in the tutorial example:
>
> &FORCE_EVAL
>     STRESS_TENSOR ANALYTICAL
>     ...
> &END FORCE_EVAL
> ...
> &MOTION
>   &MD
>     ENSEMBLE NPT_I
>     STEPS 200000
>     TIMESTEP 1.0
>     TEMPERATURE 300
>     COMVEL_TOL 1.0E-10
>     &BAROSTAT
>       PRESSURE 1.01325 #[bar]
>       TIMECON 1000
>       VIRIAL XYZ
>       &THERMOSTAT
>         TYPE SAME_AS_PARTICLE
>         &CSVR
>           TIMECON 200
>         &END CSVR
>       &END THERMOSTAT
>     &END BAROSTAT
>     &THERMOSTAT
>       TYPE CSVR
>       REGION MASSIVE
>       &CSVR
>         TIMECON 200
>       &END CSVR
>     &END THERMOSTAT
>     ...
>   &END MD
>   ...
> &END MOTION
>
> The Cons Qty in the .ener file converged after about 20 ps. However. when 
> I perform the same simulation from scratch in the NPT-F ensemble (by 
> changing the NPT-I to NPT-F), the Cons Qty kept increasing and exploded 
> after about 80 ps (please see the plot below, so are the kinetic energy and 
> potential energy). I will need the NPT-F in future for a tetragonal 
> covalent organic framework system. Could someone please let me know if I 
> had any wrong or missing parameters? 
> And a relevant question, while I set the time constant to be 200 for the 
> CSVR thermostat of the barostat, the corresponding TIMECON in the restart 
> file has a value of ~9.6755. Is that relevant to my question? I'm using the 
> version 2024.2. 
>
> And helps and discussions are greatly appreciated.
> Zhuoran
> [image: t300.png]
>

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