Hi All,
Is there any command in LAMMPS to detect the empty spaces in the simulation box? For example, the vacuum spaces on top of the simulation box.
Thanks,
Atefeh
Empty in this context is not a well defined property. Since you are simulating point particles, which have no volume, technically your entire box is empty.
What you can do and what you probably are after, is to determine the minimum, maximum x, y, or z coordinate across all atoms or a group of them, which can be done using the compute reduce command, and compare this to the locations of the upper and lower box boundary, which can be accessed at thermo properties. Please see the documentation for details.
Axel.
Hi Axel,
Thanks for your guidance.
I don’t want to compute the vacuum region; I want to change this region during the run time.
I am modelling solvent evaporation. For this purpose, I defined a region on top of the simulation box called Evaporation region. When the solvent molecules reach into this region, they are deleted. However, during the evaporation, the surface of the solution is coming down, and the distance between the solution surface and the Evaporation region is increasing. This distance makes the process slower. I want to know if it is possible to increase the Evaporation region during the run time automatically to make the evaporation process faster.
Thanks,
Atefeh
Please note that had you been given this explanation right away, instead of asking for some specific detail, you would have saved yourself and me time and effort.
Once particles or molecules are drifting away from the surface they should be doing so at a constant rate and velocity, and thus it should not make that much of a difference in time whether you adjust the evaporation region or not. That you feel it impacts your simulation time is an indication of two things: a) you have a load balancing issue and should be adjusting the domain decomposition with the processors command so that you don’t have empty subdomains (assuming you are running in parallel, that is), b) your initial evaporation region is too large and/or too close to the liquid phase, so that you initially are deleting atoms or molecules that have not yet sufficiently broken free from the interface. You want to have some distance between the interface and the region what you can safely assume, that a particle or molecule will no longer interact significantly with the liquid phase and will not return. Therefore it seems to me you are worrying about the wrong problem and trying to optimize something that is better left alone and you are not worrying enough about correctly representing the physics in your model.
That said, based on the information i gave you, it should be possible to do what you are asking for by breaking down your simulation into chunks and in between change the box dimensions and recreate the evaporation region for the new box. But as I mentioned before, I suspect that you are negatively impacting the validity of your results by trying to speed it up.
Axel.