Neigh_modify exclude

LAMMPS LAMMPS General Discussion
1

Hello
In addition to LJ, I used the following forcefield in the simulation. In tersoff pair style I defined C-C interaction and in meam C-Ti and Ti-Ti interaction, so is it necessary to exclude C-C interaction in meam pair style using neigh_modify exclude as below?

pair_coeff * * tersoff SiC.tersoff C NULL NULL NULL NULL NULL # C-C

pair_coeff * * meam FeTiClibrary.meam Fe Ti C FeTiC.meam C NULL NULL NULL NULL Ti # Ti-Ti & Ti-C
neigh_modify exclude type 1 1

Likewise for the interaction of other atom types in my simulation:

pair_coeff * * meam library.meam Ti N TiN.meam NULL NULL N NULL NULL Ti # Ti-N
neigh_modify exclude type 6 6
neigh_modify exclude type 3 3

pair_coeff * * meam libraryo.meam Ti O library.meam_alloy NULL NULL NULL NULL O Ti #Ti-O
neigh_modify exclude type 6 6
neigh_modify exclude type 5 5

pair_coeff 3 3 lj/cut 0.00314 3.32 # N-N
.
.
.
and so on

2

What you are doing is bogus and in complete ignorance of the underlying physics of the models in use and the documented behavior of LAMMPS:

The two biggest offenses are (there are more):

  • all EAM based methods (that includes MEAM) need the contributions from all neighboring atoms to correctly determine the embedding term of the model. With pair style hybrid, only the neighbors from the same sub-style entry are included.
  • neigh_modify exclude will completely remove interactions from all neighbor lists. The implied logic of your proposed commands is in stark conflict with how LAMMPS works.
3

I don’t understand what you mean, you mean I shouldn’t use meam in hybrid style?
I used hybrid/overlay and applied the meam pair style based on the manual explanation: “If a mapping value is specified as NULL, the mapping is not performed. This can be used when a meam potential is used as part of the hybrid pair style. The NULL values are placeholders for atom types that will be used with other potentials.”
Is it ok if I remove the neigh_modify command?

4

The documentation only worries about technical requirements. I am talking about the physics here. Even if you could make it work technically, it will produce bogus physics.

If you don’t understand my reasoning, you have a big problem and should not do this kind of simulation.