Hi，

Recently, I am doing some calculation with pair_style born-coul-long.

In LAMMPS, the form of born is , in front of D, the sign is plus. And in the examples of LAMMPS manual, “pair_coeff 1 1 6.08 0.317 2.340 24.18 11.51”, the D coefficient is given as 11.51, a positive number. I have analyzed that the parameters in this example are for NaCl systems with “real” units.

**So, in LAMMPS, the sign in front of D is plus, and D is set as positive for NaCl.**

Well, in the work of Fusi and Tomi (M. P. Tosi and F. G. Fumi, J. Phys. Chem. Solids, 1964, 25, 31) the potential form is:

and the corresponding parameters for molten NaCl are as follows:

**i.e. in the reference, the sign in front of D is plus, but the D is negative. The reference is also cited by LAMMPS. In fact, in many other references, the sign in front of D is minus and the D is positive.**

**So I think that there is some contradiction between LAMMPS and the most references, right?**

**What’s more**, when I calculate molten NaCl, if i set the parameters with metal units as follows (D is positive), I can do the calculation and reproduce the values of reference.

pair_style born/coul/long 10.0 8.0

pair_coeff 1 1 0.2640625 0.317 2.340 1.05 0.5

pair_coeff 1 2 0.21125 0.317 2.755 7 8.6875

pair_coeff 2 2 0.1584375 0.317 3.170 72.5 145.625

kspace_style ewald 1.0e-5

But if I set D as negative, thus the net effect of the last term is subtract the 8-order dispersion interaction, which is consistent with the reference, the calculation comes up with “nan”.

I don’t know why, I am confused about it and I can’t explain it.

Would you please help me?I would appreciate your help.

Thanks very much.

Jia Wang