Hello,

The easiest way I guess it would be to manually displace the atoms on your cell, and/or change your lattice parameters accordingly. You can get an estimation of how much you're straining by the difference between the original and modified lattice constants. As far as I know there is no built-in tool to do strain in QE.

Regards,

Assuming that QE has input files similar to that of other QC packages, you could automate the process suggested by Bruno Cucco by writing e.g. a linux shell script that performs a homothetic stretching of your unit cell along one or several axes. Especially if you need many scenarios to be checked, I think a script would be worth the time.

Md. Yasir Zamil

The best way is to write the bash script for changing the lattice parameters of crystals. If you want to apply the strain in the z-direction, you should change the lattice parameter in the z-direction

Thank you all for your answers.

I would add that you can calculate the elastic coefficients with the thermo_pw package. It applies the different strains to access the full elastic matrix for you.

If you need to do something else, thermo_pw can give you the Poisson's ratio to be used to apply properly the strain. You need to modify by hand or with a script the unit cell and then relax the atomic positions.

The easiest way to do the same is by changing the equilibrium lattice parameter. When you will reduce the equilibrium lattice parameter the lattice mismatch will lead to strain.

Setting

tstress = .true.

tprnfor = .true.

verbosity =..high.

will print the pressure corresponding to the given lattice constant in the scf output file.

Dear Abhinav,

The systematic way of applying strains on a structure at equilibrium is to introduce a small tilt to the cell parameters. This method is used to calculate the elastic constants. The method is fully discussed in the usergude of Thermo-PW code by Andrea Dal Corso.

If you want do this manually, you should change the celldm(1) manually and put ibrav=0 as well as put the cell vectors in a new symmetry situation, otherwise, Thermo_PW will do it automatically.

Pooja Vyas you have the choice of using ibrav=6 and then define a and c or using ibrav=0, a=5.07858 and

CELL_PARAMETER (ANGSTROM)

5.0785841942         0.0000000000         0.0000000000      

  0.0000000000         5.0785841942         0.0000000000    

    0.0000000000         0.0000000000         7.2853422165

In the second case, each line that follows CELL_PARAMTERS is a vector, so you need three components.

Usually using the appropriate ibrav allows the code to work best with symmetries.

Regards,

Roberto

What should be the calculation type "scf" or "vc-relax"?

@Ashwani It should be 'relax' as you want the atoms to find a local equilibrium with the new cell parameters. 'vc-relax' should bring your system back to the optimal configuration with not strain.

Regards,

Roberto