Question on Elastic constants

Dear Axel, Steeve, Aidan, and LAMMPS users,

Hi,

I’m working on Silicon nitride system which has a hexagonal crystal system with monoclinic lattice using Tersoff potential. I first build a cubic super cell and tried to use " Elastic constant Example codes " available in LAMMPS directory. It gives me almost correct elastic constants except C33, It should be 540GPa. But, I’m obtaining it as 7000GPa !!! Any comment would be really appreciated.

Sincerely,

Ali