Dear Megha

the simplest way to applied a strain in a cubic structure along the x direction (i think it will be the [100] axis) is to change the lenght of the a lattice constant in this direction by applied a small deformation e=da/a.

Dear Mohamed Ali Lahmer

Thanks alot for your reply.

It means cubic structure will change to tetragonal structure and we have to use ibrav=6 in quantum espresso?

Dear Megha

Materials Square(https://www.matsq.com) provides various tools for manipulating atomic structure including strain, vacuum and atomic manipulation tools.

You can easily make crystal structure and input script for QE.

Procedure is simple:

Add your structure using 'Crystal builder' or upload structure file, and give strain as you want using 'Strain' menu.

This picture is give strain 100% to x-axis to silicon unit cell, so the x-axis length became double.

Dear Malg,

Thanks alot for your reply. It was a great help.

The one of the simplest way to apply strain is just compress or elongate the axis. for example if the original lattice constant is 7 angstrom then to apply strain you can compress it example 6.8 and can check the pressure at 6.8 angstrom.

Abhinav Nag thanks for your answer.

But what about atomic positions?

Dear Joseph Wang

Yes. Apply strain to one axis, and give strain again to another axis.