Hi,
I want to investigate systems such as Al-Si. I have the eam potential file for Al, and tersoff for Si (Al-Al and Si-Si are thus available). Therefore, a hybrid pair-style can be used. However, I do not have the interaction potential between Al and Si.
What options I have, and what solutions lammps presents to the users in such cases?
Thanks
Hi,
I want to investigate systems such as Al-Si. I have the eam potential file
for Al, and tersoff for Si (Al-Al and Si-Si are thus available).
Therefore, a hybrid pair-style can be used. However, I do not have the
interaction potential between Al and Si.
you are missing one very important step in your logic. if you have an
Al-Si alloy, you *should* not use a hybrid pair style. both, EAM and
Tersoff have force terms that depend not only on the individual pairs, but
also on neighboring atoms. those will be missing with a hybrid pair style
and thus you are running a high risk of producing a garbage simulation
unless you have a separate Al area and an Si area and only a rather small
contact area, where you can use a pair-wise additive potential (e.g.
lj/cut) as an approximation for the inter-style interaction. for
"machining" or "impact" simulations, where mostly the repulsive cross
interactions matter, this is a reasonable approximation.
What options I have, and what solutions lammps presents to the users in
such cases?
if your case matches, the scenario described above, you can look up
"generic" lj/cut force field parameters and move on. for pretty much any
other scenario, you *need* to find a potential/force field set of
parameters from the literature, that covers your *entire* system. pair
style hybrid would result in too large a systematical error.
please keep in mind, that LAMMPS primarily provides the functional form.
there are far too many parameter sets available to bundle them all with
LAMMPS.
axel.
Thanks very much Dr. Axel for your nice explanations. I appreciate your time.
Luckily, for my case, an alloy is not formed.
May I know what you exactly mean by ““generic” lj/cut force field parameters” ? Do you mean determining sigma and epsilon parameters of the LJ potential using DFT calculations?
Regards
X
Thanks very much Dr. Axel for your nice explanations. I appreciate your
time.
Luckily, for my case, an alloy is not formed.May I know what you exactly mean by ""generic" lj/cut force field
parameters" ?
there are "general force fields" out there.
Do you mean determining sigma and epsilon parameters of the LJ potential *using
DFT calculations*?
no. that would be overkill.