# lj parameters

Dear Lammps users,
I found out that I should convert the r min in charmm22 force field which I obtained from article, but there is still a concern why the formula form in the article that I use have this difference:

{eps ij [(rmin ij/r ij)^12 -(rmin ij/r ij)^6] + q i q j/r ij} === this formula is in the article.
the correct formula for rmin at CHARMM22 force field is( a 2 is missing):

eps ij [(rmin ij/r ij)^12 - 2*(rmin ij/r ij)^6].

So I am not sure that I should use this conversion:

1-rmin ij = (2)^1/6 *sig. ij

or because there is no two beside the second term, I should use another conversion(what?).

Excuse me for several messages, the previous messages were not clear, and I am sorry for that.

Thanks

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Most of the confusion seems to arise over whether or not there was a typo in the article. Maybe it makes more sense to contact the authors to double-check with them. I canâ€™t imagine this not being a typo, but hey, you never know.

If it is a typo and they meant to write epsilon*((r_min/r)^12 - 2(r_min/r)^6), then yes, you need to perform the conversion from r_min = 2^(1/6) sigma to sigma, because LAMMPS uses the 4 epsilon ((sigma/r)^12 - (sigma/r)^6) form.