[Pw_forum] Relax calculation

Sohail Ahmad sohailphysics at yahoo.co.in
Fri Apr 25 23:14:51 CEST 2014

I am using QE 5.0.2 and I have a very basic question.
To optimise the structure of a material, i started with known experimental lattice constants and calculated energy vs lattice to know the optimised lattice constants. 

Now i wish to apply the strain 

so i increased lattice constant 'a' by 2% (let us say)

now i need to relax (i believe) to get optimised coordinates before proceeding further and wish to know force and stress as well.

So my question is i should consider it as 'relax' or "vc relax"
if relax then following should work but unfortunately no

tprnfor = .TRUE.
tstress = .TRUE.
ion_dynamics = 'bfgs'

If i donot consider force and stress, then it gives me final coordinates

Is the above step true in this particular set of problems of strain application or should i use variable cell.
i am little confused.



Sohail AhmadKing Khalid University
Abha, Saudi Arabia

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