Hi all,
I want to model a pure nano-crystalline copper with a spherical void (filled up with He) inside Cu matrix. I intend to set pressure of 1 GPa for the He-bubble. However, I’m using EAM for Cu-Cu and for the other interactions, a two-body potential reported in the literature has been employed. For equilibrating the model, I’m using NPT integrator for the two groups separately.
It’s an error to use fix npt more than once. I thought the code
checked for this and at least issued a warning, but I don’t see it.
The reason is that each fix npt will change the box size. You don’t
want to do that twice per timestep.
I don’t even see conceptually what you are trying to do with
setting one pressure for Cu and another for He. The only way
NPT “sets” the pressure is by adjusting the box size. How
can one box induce different pressures on 2 different kinds of atoms?
Also, the pressure computation in LAMMPS, is not by group.
It is always the pressure of the entire system.
Steve
Dear Dr. Steve Plimpton,
I’m trying to reproduce one published paper (http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b00864), where the authors have mentioned that depending on the different He-bubble pressure inside the Cu matrix, they observed different mechanical properties, e.g., dislocation movement.
In the supplementary document (attached and highlighted) they state that “For the model with He bubbles, three 5 nm He bubbles with 1 GPa He gas pressure inside are placed along X directions.”
I’ll definitely contact the authors, but, before that I just would like to ask lammps users and developers how I can model this He-bubble with different pressure inside copper ?
I appreciate any suggestion/idea in this regard.
Thanking you.
-Cheng
nl6b00864_si_001.pdf (624 KB)
Dear Dr. Steve Plimpton,
I'm trying to reproduce one published paper (http://pubs.acs.org/doi/abs/
10.1021/acs.nanolett.6b00864), where the authors have mentioned that
depending on the different He-bubble pressure inside the Cu matrix, they
observed different mechanical properties, e.g., dislocation movement.
In the supplementary document (attached and highlighted) they state that
"For the model with He bubbles, three 5 nm He bubbles with 1 GPa He gas
pressure inside are placed along X directions."I'll definitely contact the authors, but, before that I just would like to
ask lammps users and developers how I can model this He-bubble with
different pressure inside copper ?
you just need to remember basic thermodynamics: look at the ideal gas
equation p*V = nRT and divide by V so you get: p = nRT/V . now it should
be obvious, that you have 3 variables, that you can change to change the
pressure: n, T, and V. since T and V do not make sense in this context, you
will have to modify n until you have the desired pressure.
axel.
Hi Cheng,
if there is 1 GPa inside the bubble, there will be isotropic 1 GPa in copper, too. It follows from equilibrium of the bubble boundary. So you can impose the desired pressure on the whole MD cell.
Regards,
Oleg
07.04.2017, 15:58, “Batista Cheng” <batistacheng4@…24…>: