### Symmetries 

The elastic constants tensor obtained should reflect the symmetries of the crystal structure of the material in question. This [comment article][1] can be a helpful reference. Elastic constants that do not reflect the crystal symmetries could indicate that the DFT calculations are not converged enough, or that your strains are too large.

### **Convergence**

 This is somewhat related to the above (symmetries could be a sign of poor convergence). Generally, you could also redo calculations on finer settings (higher plane wave cutoffs, k-point sampling, etc) and check if the elastic constants change by much. It could also be a good idea to vary the maximum strain you are using for the stress-strain elastic constants calculation to check how sensitive your results are to it.

  [1]: https://iopscience.iop.org/article/10.1088/2053-1583/ab2ef3