# Tersoff potential question

Hi,

I have read the LAMMPS documents on Tersoff potential carefully but I can’t figure out the element entry order.

We have three element entries where the first element is the central atom, which corresponds to atom i in Tersoff papers.

Do the second entry and the third entry correspond to atom j and atom k in Tersoff papers, respectively?

I am a little confused as available Tersoff potentials in LAMMPS tend to use ikj notation.

For example, R_i,j is given by (R_i * R_j)^0.5. Therefore, we would expect that C-C-Si has the same R_i,j as the one in C-C-C if the element entry order was i,j,k. However, they are not. Instead, it seems like the element entry order is i,k,j in all the multi-atom Tersoff potentials given in LAMMPS.

Could you please clarify the element entry order?

Thanks,

Jay

Hi,

I have read the LAMMPS documents on Tersoff potential carefully but I can't
figure out the element entry order.

We have three element entries where the first element is the central atom,
which corresponds to atom i in Tersoff papers.

Do the second entry and the third entry correspond to atom j and atom k in
Tersoff papers, respectively?

I am a little confused as available Tersoff potentials in LAMMPS tend to use
ikj notation.

For example, R_i,j is given by (R_i * R_j)^0.5. Therefore, we would expect
that C-C-Si has the same R_i,j as the one in C-C-C if the element entry
order was i,j,k. However, they are not. Instead, it seems like the element
entry order is i,k,j in all the multi-atom Tersoff potentials given in
LAMMPS.

Could you please clarify the element entry order?

the details about the file format are given in the tersoff pair style
documentation. if you are confused and need confirmation, perhaps you
should look up the publication for one or more of the potentials that
are bundled with LAMMPS and compare the potential files with the
information in the paper. if needed, check the source code, too.

axel.

Forwarding to Aidan, in case he has a comment.

Steve