[QE-users] How to appropriately relax or vc-relax structure under strain respecting Poisson's ratio

[Karkee, Rijan]

Hello QE community,

I am trying to study the material under uni-axial strain.  I put the atomic coordinates in crystal coordinate and then apply the strain to the lattice vectors.

For example,
If S is my original (unstrained) lattice vectors:
array([[ 1.98619742 ,  7.132231003,  0.         ],
       [-1.986197815,  7.132230891,  0.         ],
       [ 0.         ,  0.         , 13.586526936]])

Then applying 1% strain (tensile) to S along x-axis, would result
Strained_lattice=array([[ 2.0060593942,  7.132231003 ,  0.          ],
       [-2.0060597931,  7.132230891 ,  0.          ],
       [ 0.          ,  0.          , 13.586526936 ]])


After this lattice determination, I want to relax (or vc-relax) structure in such a way that it respects Poisson's ratio (keeping constant Poisson's ratio).

My question is:


  1.
Do I just "relax" the structure? or
  2.
"vc-relax" with cell_dofree=
'fixa'
  3.
Or which cell_dofree would be appropriate?

Thank you.


Best
Rijan Karkee


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