[lammps-users] how can i change a density of atoms?

Hello,

I try to simulate a flow on solid layer.

So, i have two regions, for layer and for flow. These regions have different densities.

The question is how can i change a density of flow's atoms? Parameters of simulation box have to be constant.

Sergey R.

Dear all,

I have built recently a similar system, and a nice way to do this
would be to create all atoms on the solid lattice, and then to use the
delete_atoms command with keyword porosity to adjust the density of
liquid atoms.

However this solution is not fully satisfying currently because "There
is no guarantee that the exact fraction of atoms will be deleted" by
this command.

I've had a similar issue with the set type/fraction command when
trying to prepare a solvent/solute system with a precise solute
fraction.

Therefore I was wondering if there was a reason for not
setting/deleting the exact requested fraction of atoms, as this would
be a real improvement for the kind of problems I discussed.

Best regards,
Laurent Joly

2010/5/30 Romashevsky S. <[email protected]>:

You can use the lattice command once to define a box size and
create one set of atoms at a particular density. Then you can
use the lattice command a 2nd time (or 3rd time, etc) to create
a new set of atoms at a different density, in a different region).

Steve

Therefore I was wondering if there was a reason for not
setting/deleting the exact requested fraction of atoms, as this would
be a real improvement for the kind of problems I discussed.

I don't recall exactly, but I think it has to do with how to find atoms
to delete that meet the criteria and coordinating that across processors.
Easy to get close to the desired answer, but hard to be exact.

As a fallback, you can always generate the input you want yourself,
and just input it as a data file of coords.

Steve