Hello
I want to set up a case (Solid, liquid and vapor) with constant temperature using NVT. After equilibration, I want to change the pressure of vapor region only ( increase / decrease from saturation condition) and observe the liquid behavior. Is this possible to set up such cases? Need experts opinion on that. Thank you.
Hello
I want to set up a case (Solid, liquid and vapor) with constant temperature
using NVT. After equilibration, I want to change the pressure of vapor
region only ( increase / decrease from saturation condition) and observe the
liquid behavior. Is this possible to set up such cases? Need experts opinion
on that. Thank you.
well, you can just vary the simulation cell volume accordingly.
axel
Dear Dr. Kohlmeyer
To decrease pressure,I found a paper where they set up a deletion region, from where they remove atoms after a certain time steps. There method seems better, but is that easy to write a command in the script file or do I need to do this manually. Please let me know at your convenient time. Thank you very much.
Dear Dr. Kohlmeyer
To decrease pressure,I found a paper where they set up a deletion region,
from where they remove atoms after a certain time steps. There method seems
better, but is that easy to write a command in the script file or do I need
to do this manually. Please let me know at your convenient time. Thank you
very much.
i'd say both options are somewhat equivalent. whether you expand the
cell or remove atoms, you adjust the density and thus influence the
pressure.
also, both are inconvenient when they get to the extreme (too few
atoms for left for good statistics vs. too large a volume for
efficient parallelization).
in LAMMPS you can break down a long run into sections, i.e. use
multiple run commands, and perform commands like delete_atoms or
change_box in between. you can also wrap this into a loop. if you want
the best of both worlds, you'd start with a high density gas phase and
delete atoms for a while and then switch to expanding the box, so you
have a reasonable minimum number of gas phase atoms.
to continue from here, you need to study the LAMMPS documentation and
examples and debug and build a suitable simulation script. it is
highly recommended to do this in stages and practice with a (too)
small system first, in order to make certain that you fully understand
what you are doing. many people make the mistake of jumping ahead too
quickly and thus struggle with unexpected and difficult to understand
(for them) errors or bogus results (often without being aware of it
until it is too late) or a combination of both.
axel.
Thank you Dr. Kohlmeyer.
One way to achieve this would be to use fix gcmc and the region keyword, so that it only adds and removes molecules only from the gas phase. You can even use the pressure keyword to specify a desired ideal gas pressure for the gas phase.