[QE-users] Elastic Constant with PWSCF in Quantum Espresso

[Stefano de Gironcoli]

you can locate the equilibrium geometry with vc_relax and then manually 
apply homogeneous deformation, relaxing the INTERNAL degrees of freedom 
and obtaining the elastic constant from the stress strain relationship. 
you will need to  apply +/- deformations of various strength and extract 
the linear term in the variation of the stress tensor. Traceless 
deformations are preferable because they don't change the average number 
of planewaves. make sure your cutoff is converged for a stress calculation.

If the system has some symmetry this helps reducing the number of 
calculations needed.

For instance for cubic symmetry two deformations are enough: an e1 
deformation (voigt notation 
https://en.wikipedia.org/wiki/Voigt_notation) gives C11 and C12 and e4 
gives C44

for a generic crystal you need six deformations (e1,..,e6) to get the 21 
independent elastic constants.

stefano

On 29/03/25 15:03, Jonathan Konyi Kakulu wrote:
> I have get bulk modulus with ev.x . I want to know how to calculate 
> the C11, C12 and the C44 constant with PWSCF
>
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