BMH potential parameters

Hi there,

I’m recently trying to use BMH potential for calculating elastic properties of KCl. According to the lammps website (http://lammps.sandia.gov/doc/pair_born.html) , the last parameter D should have a POSITIVE sign. However, in some other papers such as: Aragones, et al , J. Chem. Phys. 137, 104507 (2012)., D has a NEGATIVE value.
I didn’t see any paper that uses this potential to calculate the elastic constants, so without comparison I’m not sure which sign is correct. Can anyone help confirm with me whether D should be positive or negative?

Thanks,

Chun