[CP2K-user] [CP2K:20013] Challenges with NPT Dynamics Simulation

[Xiangru Tan]

Hi everyone, I'm working on simulating the NPT ensemble dynamics of crystal 
materials aiming for a target temperature of 300K with CP2K version 2023.1. 
Initially, I planned to run the simulation for 1000 steps over 500fs. 
However, I encountered an issue at step 802. Fortunately, I haven't lost 
any data from those first 802 steps.

 

Here are the details on the temperature changes and the changes in the 
supercell volume:

 

I've also included the input file (with coordinates removed) and the output 
file (I've omitted repetitive information at the midway point).

 

Here are my questions:

1) There were no error messages in the output file. Could someone help me 
figure out what went wrong?

2) The temperature seems to plateau at 232.6K, despite my setting it to 
300K. I understand that I might not have completed enough steps (missing 
nearly 200 steps), and the heating time constant might be set too high (300 
fs, with 400 fs already completed). However, shouldn't the temperature 
still continue to rise?

3) Why does the volume keep increasing even when the temperature stops 
rising? What could be causing the volume to continuously expand?

 

Additional Insights:

1) I've conducted simulations on several structures with identical 
parameters, encountering similar issues across the board. This suggests the 
problem isn't just a random occurrence. Some simulations completed, while 
others, like the one in question, nearly didn't. Notably, simulations that 
didn't complete showed no error messages. However, completed or not, none 
of the simulations achieved the target temperature, and all experienced a 
continuous increase in volume.

2)The simulations are based on experimental crystal structures and were 
directly subjected to dynamic simulations without prior optimization. 
Although there was no disintegration of the structure, there was a 
noticeable, consistent increase in the distance between molecules, 
suggesting expansion.

 

Thanks for any insights you can provide.

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