Dear LAMMPS users

The question about units in EAM potential files was here already

(http://sourceforge.net/mailarchive/forum.php?thread_id=26117938&forum_id=46682).

But I met same problem as in that message. When I try my own potential

file I obtain very large values of energy and pressure. To find origin of

the problem I performed simple test.

At first I wrote simple potential file:

Test potential

47 107.868 1.00 FCC

20 1.0e+00 10 0.1e+00 0.9e+00

0.0e+00 1.0e+00 2.0e+00 3.0e+00 4.0e+00 5.0e+00 6.0e+00 7.0e+00

8.0e+00 9.0e+00 10.0e+00 11.0e+00 12.0e+00 13.0e+00 14.0e+00

15.0e+00 16.0e+00 17.0e+00 18.0e+00 19.0e+00

0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00

0.0e+00 0.0e+00

0.0e+00 0.1e+00 0.2e+00 0.3e+00 0.4e+00 0.5e+00 0.6e+00 0.7e+00

0.8e+00 0.9e+00

There are only attractive part of potential in this file. Then I

calculated energy per atom for FCC lattice with lattice parameter 1.0. It

was OK I obtained expected value -8.48 eV

Then I change this potential file to put there only repulsive forces:

Test potential

47 107.868 1.00 FCC

20 1.0e+00 10 0.1e+00 0.9e+00

0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00

0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00

0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00

1.0e+00 1.0e+00 1.0e+00 1.0e+00 1.0e+00 1.0e+00 1.0e+00 1.0e+00

1.0e+00 1.0e+00

0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00

0.0e+00 0.0e+00

I expected to get energy per atom as 6 eV (0.5*12*fi - where 12 is number

of neigbours) but I obtained 122.09 eV. It is certainly very large value

and certainly it results in large pressure. So I can conclude that

something wrong with repulsive forces in potential file but I don't

understand what exactly.

I will appreciate for answers.

Sincerely yours

Andrey Ostapovets