Question on Elastic constants

Dear Axel, Steeve, Aidan, and LAMMPS users,


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.