# How to implement the Flohais pseudopotential for NaK alloy MD simulation in LAMMPS

Dear all,

I would like to simulate the physical properties of NaK alloy liquid and vapor using MD simulations. However, there lacks appropriate potential for NaK alloy. I found that Wax, J. F. et al. adopted the Fiolhais’ pseudo potential and the results seem to be great. Please see following literatures about the potential:

(1) Fiolhais, C., Perdew, J. P., Armster, S. Q., MacLaren, J. M., & Brajczewska, M. (1995). Dominant density parameters and local pseudopotentials for simple metals. Physical Review B, 51(20), 14001.
(2) Becker, S., Meyer, N., Xu, H., & Wax, J. F. (2020). Viscosity of liquid Na–K alloys from molecular dynamics simulations. Journal of Physics: Condensed Matter, 32(19), 194005.

My question is if it is feasible and how to implement the Fiolhais’ pseudo potential in LAMMPS. Any suggestion or comment would be highly appreciated.

Best regards,
Huaqiang

You could evaluate the force landscape at your phase point of interest and then use `pair table` to implement it.

Thank you for your reply. What do you mean by “evaluate the force landscape”? It would be really appreaciated if you could explain more about the detailed methods. I’m not familiar with the pair force development.
Thanks again for your kind help!

Pseudo potentials are used with quantum mechanical software that computes forces from the electronic structure. LAMMPS is not such a software. It uses more approximate models. At any rate, you would have to write C++ code (and quite a bit) to make those potentials work. Tabulation would only work if the interactions would be purely pairwise additive.

See: pair_style table command — LAMMPS documentation . What I mean is just to calculate what the force and energy is at every interatomic distance and put it in a table.

And as Axel said, this will only work if the forces are purely additive and radial (i.e. the force on any particle is the sum of two-particle forces, each of which only depend on the distances between particles). There is a three body table style which you could use for three body forces, but I don’t know if that will suit your needs either.