Fix rigid, deposit and temperature instability

lammps version: lammps-23Jun2022

My system consists of both rigid and non-rigid components. To handle the non-rigid part, I employ the “fix nvt” command.
For the rigid section, I utilize “fix rigid/nvt/small” along with “fix_modify dynamic/dof”.

Additionally, I use “fix deposit” to introduce new molecules into the system, alongside “fix nvt” to maintain stability.

However, after introducing the third molecule via “fix deposit,” the system’s temperature rises from room temperature to 600K, leading to vaporization. It seems I may have overlooked a crucial detail. Any advice would be greatly appreciated.

But since your description is rather vague, nobody here can tell you what the detail would be.

I will try to make it clear:

My system consists of Na2SO4 + H2O!
For water (is rigid by “fix shake”) and Na ion I use “fix nvt”
for SO4 I use “fix rigid/nvt/small” + “fix_modify dynamic/dof”
I can do NVT simulation on this system with no problem!

On the other hand I use “fix deposit” and add one non-rigid molecule to the surface of the current system:
“fix deposit” to insert the molecule and “fix nvt” for the time integration.
adding this molecule to my current system causes temperature instability! It increases from 300 to 600K!

This doesn’t clarify anything.

Which non-rigid molecule?

What do you mean by “to the surface”?

It is your system, you know what it looks like, you can determine how the system is changed and whether that makes sense.

What you are asking for is that somebody else does your job. If you do something and then the system becomes unstable, you have to develop hypotheses of what could be causing this, of course you look specifically at the inserted molecule and where and how it is placed into the system.

Nobody from the outside can really help you in the way you are asking for without being closely familiar with your research and having access to all the files and looking at the output of your failing runs.

You seem to expect that there is this “magic” command or setting that you add to your input deck and then suddenly everything will work. LAMMPS will just do what you tell it to do and it is your job to tell it the right things. So if you have trouble with inserting molecules into a complex system, you perhaps should set up a simpler system and perhaps only insert atoms. Once you figured out how to do this in a meaningful way, then you can graduate to inserting molecules and then perhaps insert atoms into your complex system before finally combining what you have learned from the various exploratory simulations to build the simulation input for the system you want to simulate.

This doesn’t really address the issues that make it extremely difficult to provide more detailed assistance. I think I have said all I want to say and you have exhausted my contingent of goodwill (mostly with forcing me to ask for things I should not need to ask for) anyway, so it is time that you do some thinking and and problem solving on your own.

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