ERROR: Lost atoms


my system works for a temperature of 10K. However for T=300K I have the following error

ERROR: Lost atoms: original 43688 current 43609 (src/thermo.cpp:438)

What could I do?

Please note that you have an extremely high pressure. That is usually an indication that you have a bad initial geometry or a bad model with unsuitable potential parameters or both.

The fact that you can run at 10K doesn’t indicated anything, because you a) have set a tiny timestep
(for elements like C O N you should be able to use 1fs instead of 0.1fs even at 300K) and b) not much happens at a low temperature of 10K, so your system can remain in some meta stable state.

A bad geometry with close contacts can often be relaxed by running a minimization before starting an MD. If that does not help you likely have problems with your model.
In case of problems it is also advisable to output thermodynamic data and trajectory more frequently, so you can observe which properties are at unusual values during minimization or MD and which atoms move unexpectedly.

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The problem was that it used repulsive LJ-type walls and the wall was too close to the edge of the box. The reflective walls solved the problem. It would be possible to use the Fix Wall with the repulsive potential of LJ, but I would have to CORRECTLY adjust these walls.

Thank you so much, Axel.