[lammps-users] Gas atmosphere modelling


I am trying to simulate a case with a gas atmosphere. I want the molecule to be amorphously aligned so that it can mimic the real environment. Is there any idea to reach the amorphous model?


How large a system and what kind of gas at what kind of density/pressure?
What “molecule” are you talking about?
Perhaps it is better you explain in more detail what kind of system you want to model and what role that gas has in the process.


I want to have hydrogen gas as the environment of a system with 1 atm and room temperature. The scale I design at first of 50000 H atoms

At 1atm and room temperature you can approximate the density of hydrogen (or any simple gas) with that of an ideal gas.

I suggest you do the math and compute how large a box you would need for 25000 hydrogen molecules.
If this gas phase is supposed to be in contact with some other atomic system, e.g. a metal surface, there is not much of a difference between a gas at 1atm and room temperature and a vacuum. you probably wouldn’t be able to simulate a system large enough to make a difference and any interaction of the gas with the surface would be infrequent.
On the other hand, you won’t need to worry much about equilibration, you can just assign some random kinetic energy to the atoms according to the desired distribution and place the molecules on random positions in a suitable region and you won’t have to do a complex equilibration like for a liquid.

The gas atmosphere is only becoming a significant factor in high-pressure environments and thus much increased densities.