[QE-developers] Significant Deviations from Elastic Tensors from existing codes

Tue Feb 12 13:49:44 CET 2019

Dear Developer(s),

I have encountered what would appear to be a serious bug in your code. I have been trying to tabulate some elastic constants for Si and Cu only to realize that your code has some issues with some components of the elastic tensor.

Namely, the c44 component of Si and c11 component of Cu. All my other parameters are within a reasonable range of existing VASP calculations.

For example Si (in GPa):
Component
        Materials Project (VASP)
        ESPRESSO with the same routine as Materials Project (I did these calcs)

c11
        144
        156

c12
        53
        62

c44
        75
        104

I have converged my cutoff parameters and kpoint mesh. I also tried fiddling with the tolerances on energy and forces. All of these are converged in the values I show you above. It would seem both your energies and forces are miscalculated in certain deformation directions (and no I did not apply too much of a deformation). I am fairly certain that these issues have nothing to do with my code as I also implemented it for CP2k and the results were within acceptable margins of existing code.

If you require any more information to assist you in this effort, let me know.

CHRISTOPHER PASHARTIS

PhD Student in Computational Materials

christopher.pashartis at imec.be<mailto:christopher.pashartis at imec.be>  I  www.imec.be<http://www.imec.be/>

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