Hello all,

I am trying to calculate the elastic constants of cementite (Fe3C) with Quantum Espresso using inputs generated by ElaStic. However, when I call ElaStic, I have as output:

Number and name of space group: 2 (P -1)
Triclinic structure in the Laue classification.
This structure has 21 independent second-order elastic constants.

But cementite is orthorhombic with 9 independent elastic constants. sgroup is not able to classifiy it correctly because I entered the conventional unit cell (below)? Thanks in advance.

ATOMIC_POSITIONS crystal
C -0.119491674 0.249982623 0.441808604
C 0.119491674 -0.249982623 -0.441808604
C -0.380404252 -0.249973646 -0.057798324
C 0.380404252 0.249973646 0.057798324
Fe 0.041910120 0.250056375 -0.159219104
Fe -0.041910120 -0.250056375 0.159219104
Fe 0.457866115 -0.250061254 0.340943503
Fe -0.457866115 0.250061254 -0.340943503
Fe 0.183569742 0.068664582 0.331995453
Fe -0.183569742 -0.068664582 -0.331995453
Fe -0.316534124 0.431316546 0.168056629
Fe 0.316534124 0.568682454 -0.168056629
Fe -0.183592774 0.568754219 -0.332024228
Fe 0.183592774 0.431244781 0.332024228
Fe 0.316559314 -0.068592706 -0.168095176
Fe -0.316559314 0.068592706 0.168095176

Best regards,

Roberto