MEAM screening parameters

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1

Good day LAMMPS users,
I was making some simulations on a binary alloy and according to some papers the directions for the screening parameters in this kind of alloys are AAB, ABB, ABA & BAB, to fit other values I try to find a right combination of these parameters, recently as a mistake I valuated another potential file which included the BAA direction that is suppose to be the same as BBA, then one of these directions was omitted, trying it the result was totally different compared with the one with both directions, I tought that maybe because it was overwriting the other but still no matter the combination I can’t get the same results as the original one.
So my question is it’s right to include BAA & AAB the same as ABB & BBA that are suppose to be the same? I am working with a monoclinic structure of a binary alloy.

Thank you for your help and comments,

Mario Muralles

2

I’m not clear what you are asking. If you are asking about the
details of the format of a MEAM potential file, then Greg Wagner (CCd)

is your best bet. If you’re asking something else, then
you need to clarify.

Steve

3

Thank you for answer!
Sorry for not being so clear, my question is not regarding to the format, is about the screening parameters, here are my cases,

  1. As a paper says “a total of eight parameters of Cmax and Cmin (A-A-B, B-B-A, A-B-A, A-B-B) are needed for binary AB alloys”.

  2. But if I include more parameters like BAA that should be the same as AAB the same as ABB and BBA (for binares), the results change.
    So my question is should I take in account these parameters? and furthermore what can be the reason that this happens? just as a reference I am working with a monoclinic structure.

Thank you for your help!

4

I don’t know. I suggest you ask the author of the
paper.

Steve

5

Mario,

Note that in the LAMMPS MEAM potential file, the last index (k)
designates the atom that is *between* the atoms i and j (i.e.screening
atom):

Cmax(I,J,K) = Cmax screening parameter when I-J pair is screened
              by K (I<=J)
(See http://lammps.sandia.gov/doc/pair_meam.html)

The MEAM pair potenital file should work if you include only screening
parameters with i<=j (remaining screening parameters are deduced from
symmetry).

Here are some working examples:
http://www.ctcms.nist.gov/potentials/Al-Si-Mg-Cu-Fe.html
http://code.google.com/p/ase-atomistic-potential-tests/

Best,
-Bohumir