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.