How to use a new potential in LAMMPS

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1

Dear all,
     I want to use a new potential, which adds a electrostatic term after
the tersoff potential, HOW do I implant this new potential?
     I will appreciate it if you can give me any suggestions!

Best wishes,
XJ

2

See doc/Section_modify.html which explains
how to add features to LAMMPS, including
pair styles.

Steve

3

Also, if this is just Tersoff + qq/r, you could
use pair_style hybrid with Tersoff and pair_style coul.

Steve

4

Thanks very much。
The partial charge on atoms is dynamic. the effective charges are
determined by an equilibrium distance, seems very complexed to be
implantated.

I will try first.

XJ

5

Dear XJ,
As Steve was saying, look at:
http://lammps.sandia.gov/doc/pair_hybrid.html

To clarify:
I think that you want to use "overlay/hybrid".

"hybrid" allows you to use different force fields for different atoms.
But "overlay/hybrid" allows you to sum two different force fields
together (on the same atoms). For example, to add the Tersoff
potential to the the long-range Coulomb potential, use something like:
"pair_style hybrid/overlay tersoff coul/long 10.0"

Cheers
Andrew

If the charge is distance dependent, then you can write a new version
of the coulomb potential.
http://lammps.sandia.gov/doc/Section_modify.html
(This sounds difficult.)
If you create a new pair_style named "NEWCOUL" (for example) then you
should be able to combine it with Tersoff using: "pair_style
hybrid/overlay tersoff NEWCOUL" (...followed by any parameters you
need, like "10.0" in the example above.)
Fortunately, I think you probably do not have to modify the Tersoff
potential code.

(I hope everything I said is correct.)

Thanks very much。
The partial charge on atoms is dynamic. the effective charges are
determined by an equilibrium distance, seems very complexed to be
implantated.
I will try first.
XJ
From: Steve Plimpton <[email protected]>

Also, if this is just Tersoff + qq/r, you could
use pair_style hybrid with Tersoff and pair_style coul.
Steve

> Dear all,
> I want to use a new potential, which adds a electrostatic term
> after the tersoff potential

HOW do I implant this new potential?

6

2011/9/6 Andrew Jewett <[email protected]...>:

Dear XJ,
As Steve was saying, look at:
http://lammps.sandia.gov/doc/pair_hybrid.html

To clarify:
I think that you want to use "overlay/hybrid".

"hybrid" allows you to use different force fields for different atoms.
But "overlay/hybrid" allows you to sum two different force fields
together (on the same atoms). For example, to add the Tersoff
potential to the the long-range Coulomb potential, use something like:
"pair_style hybrid/overlay tersoff coul/long 10.0"

Cheers
Andrew

If the charge is distance dependent, then you can write a new version
of the coulomb potential.
http://lammps.sandia.gov/doc/Section_modify.html
(This sounds difficult.)

another option to consider would be to implement a fix
similar to the charge equilibration in fix qeq/reaxc or qeq/comb
http://lammps.sandia.gov/doc/fix_qeq_reax.html

overall, there also is the COMB potential:
http://lammps.sandia.gov/doc/pair_comb.html
which sounds a _lot_ like what is described by the OP.

cheers,
     axel.

If you create a new pair_style named "NEWCOUL" (for example) then you
should be able to combine it with Tersoff using: "pair_style
hybrid/overlay tersoff NEWCOUL" (...followed by any parameters you
need, like "10.0" in the example above.)
Fortunately, I think you probably do not have to modify the Tersoff
potential code.

(I hope everything I said is correct.)

as far as i can tell, yes. :wink: