[lammps-users] Need to improve Pair_coeff command for three-body potentials

I don't understand your model. You have two types
of atoms. Which types do you want to interact
via which potential?

Steve

2009/6/3 M. Joe <[email protected]>:

I want to give following interactions:

Tersoff potential for Si-Si
Tersoff potential for Si-C
Brenner potential for C-C

Seems to be OK but we used three-body potentials so internally each calculation could be overlapped e.g. Si and C are neighbored around center atom C.

Minwoong Joe

Seems like an odd model, but you
could do it as follows. Tersoff will
need to operate on Si and C (types
1 and 2) which means it will also
compute C-C interactions since they
are in its neighbor list. But you could
effectively turn those off by editing
the SiC.tersoff file and setting coeffs
to 0.0 for three-body C-C-C and two-body
C-C terms.

Then use pair hybrid/overlay as you outlined
to apply AIREBO to just type 2 (C-C).

Steve

Thank you so much. Steve.
Could you explicitly write down the two body C-C terms in the SiC.tersoff
file?
Because I am not clear whether I can treat C Si C and Si C C as a two body
C-C terms

Best regards,

Minwoong Joe

You need to examine the Tersoff formulas
on the doc page and its description of the
format of the Tersoff file and figure out
which ones to set to 0.0. It discusses how
the 2-body and 3-body distinction is made.

Aidan, am I correct that this should be possible,
to turn "off" all 2-body C-C and 3-body C-C-C,
but leave "on" any 2- or 3-body that has a Si?

Steve

2009/6/5 M. Joe <[email protected]>:

Hi steve,

I think this is great solution and I’m also working on the same question. Following your suggestion, I modified the tersoff potential with zero two body and three body interaction of C and C. However, the error occurs as following:

p1_14021: p4_error: interrupt SIGSEGV: 11
p3_14051: p4_error: interrupt SIGx: 13

pair_style hybrid/overlay tersoff airebo 3.0 1 1
pair_coeff * * tersoff SiC.tersoff_modified Si C
pair_coeff * * airebo CH.airebo NULL C

I have never seen this before, and I checked the Error & warning messages document and there is no explanation for this. Could you tell me what is going on? Thanks!

Best,

AC

Yes, you can turn off all the C-C interations by setting the A and B
parameters to zero in the "C C C" line. I agree with Steve that this is a
questionable physical model for Si-C mixtures.

Aidan