# [lammps-users] tersoff parameters conversion b/w Tersoff_1 & Tersoff_2

Dear Steve,
I am studying the lammps manual for conversion for Tersoff potential formula 1 (lammps’s Tersoff_1) [PRB37,6691’88] and formula 2 (lammps’s Tersoff_2) [PRB39,5566’89] and still wonder about its f_c(r_ij) form are different and may not be easily converted each to other. Shorly 1st is 1/2-1/2sin(Pi/2(r-R)/D) but 2nd 1/2+1/2cos(Pi(r-R)/D).
I am asking that since I found some potential which are in either forms. Couls you make some more clarification.
Any help could be appreciate with courtesy…
Regards,
VNT

Maybe Aidan can answer this, I've CCd him.

Steve

I think they are the same, but the intervals are different.

1/2+1/2 sin(Pi/2 (r-R)/D) R-D<r<R+D

is equal to

1/2-1/2 cos(Pi (r-R')/(S-R')) R'<r<S ; R'=R-D , S=R+D

Regards,
Ali Rajabpour

Steve Plimpton wrote:

I don't understand your question(s), so let me ask you one. Have you tried
using the formulas given in the LAMMPS documentation to convert?

R=(R'+ S')/2 and D=(S'- R')/2

Aidan