I used the oscillation module in LAMMPS (fix deform) and successfully simulated CO2 bubble formation in a fluid. However, my research is about CO2 bubble formation in a fluid in a confined space. Because solid walls are present, I cannot use the oscillation module, or it had no effect when I tried it. I would like to ask if there is an alternative module that can replace the oscillation function. In a pure bulk phase, cavitation occurs in the fluid immediately when oscillation is applied. But in a confined space, I still have not found a suitable command to simulate this. Could you please suggest one?
How do you model those walls?
If you are using explicit atoms, you can move them with fix move. If you are using wall fixes, you can set the wall location with a variable and move them accordingly.
Thank you, Professor. I constructed a solid illite pore. To mimic the real situation, the pore width cannot change, and the pore can only change along the pore channel direction. I tried to seal both ends of the pore with helium plates. Then I used fix move to move the left helium plate while applying NVT to the fluid. However, it did not work. Can I use fix move to apply a periodic move to the fluid?
Sorry, but it is impossible to give meaningful advice on descriptions like “it does not work”.
You have to explain in detail what you did and how and why you made these choices, and then describe how you have determined that the outcome does not meet your expectations and what you expected instead.
I’m sorry. Let me explain more clearly.
First, I used fix addforce to compress CO2 and C8 molecules inside a solid pore at a certain ratio, so as to maintain a certain pressure. I want to simulate CO2 exsolving from the fluid when the pressure drops. The fluid becomes supersaturated, and then nanobubbles form. But lowering the pressure alone is not enough for bubbles to form. Some stretching may also be needed.
This is what I mentioned earlier: for a pure CO2/C8 system, I used fix deform together with nve, and stable bubbles appeared after some simulation time. But in a system with solid walls, fix deform cannot be used.
I tried adding helium plates at both ends of the pore. I used fix move to gradually move one plate, and I applied NVT to the fluid. No bubbles formed. I also tried using fix addforce to apply opposite forces to the fluid inside the pore, in order to mimic fix deform. Unfortunately, that failed too.
So I would like to ask if there are any commands that can do what fix deform does in this situation.
you are discarding the fact that the pore geometry versus a bulk system might impact the likelihood of bubble formation. certain density fluctuations are suppressed in a confined geometry.
you should be able to apply fix deform in the periodic dimension of your pore, but moving the wall(s) slowly so that the system can expand or is compressed should be equivalent.