Interatomic potential and user-defined potential for nanoparticle simulation

LAMMPS LAMMPS General Discussion
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1

Hi everyone,

I’m planning to run a molecular dynamics (MD) simulation of an AX nanoparticle with a specific facet (111) in a box, containing A+ and X- ions in the gas phase. I want to see the growth of nanoparticle. I need to set everything up using real/metal units.

I have two main questions:

  1. What interatomic potential would be most suitable for simulating this system? Can I find a template LAMMPS input script?
  2. How can I incorporate a user-defined potential for the AA, AX, and XX interactions if I already have the potential energy curves/data?

Any guidance or suggestions would be greatly appreciated.
Thanks in advance!
TP

2

That is a topic for a careful search of the published literature, regardless of what your elements A and X are.

Not in the LAMMPS distribution.

See pair style table. You will have to generate the force through numerical differentiation, though.

3

For, this “pair_style”, I would require a table of x, V(x), F(x) for user-defined tabulated potential

I have a table where the potential energy V(x) for each given point x. Is there any lammps script to compute force from numerical differentiation if no force function is provided?

4

LAMMPS does not do this, you need to create a suitable table with some external tool. Some examples for how to write such a tool for creating tables are given in the tools/tabulate/ folder.

5

Many thanks. Got it.
So this differentiation needs to be done by Central Difference Method.

6

No.

7

Then?
The central difference method is generally more accurate than forward or backward differences.
And it can be done by a writing a py script.

8

You can choose whatever method you prefer. Of course, different methods have differently noisy output. I usually choose a Savitzky-Golay filter to compute a polynomial for each data point based on 2N+1 surrounding data point and then use the first derivative of that polynomial (typically with N=10 and a 4th order polynomial).

It is straightforward to test the accuracy of your chosen method by comparing to the implemented analytical potentials, e.g. lj/cut or morse and use pair_write to get a table of their energy and force for a given set of parameters.