It is not difficult. Please have a look here

Fthenakis Z.G. and Lathiotakis N.N. Phys. Chem. Chem. Phys. 17, 16814 (2015)

Article Graphene allotropes under extreme uniaxial strain: An ab-ini...

Hi Zacharias,

Thank you very much for the information. I will have a look! 

Dear Daniel

What kind of computational study you are dealing with? Young modulus is the ratio of tensile strain to responding stress. You have to apply some certain strain (at a certain direction) with a reasonable rate and monitor the responding stress. Plotting strain against stress at linear region (low strain region) and 1st derivation results Young modulus.  

Dear Sayyed,

Thank you very much! It is very helpful.

I am dealing with a computational study on which a 2D organic material is stretched, and we are interested in looking at how that affects the electronic structure and related properties.

From the optimized structure we have applied an increasing strain, always in the region where the sigma skeleton of the structure is maintained and the associate energies are not too high. I guess this is what you meant by "Plotting strain against stress at linear region". The problem is that I am not sure how to actually calculate the stress- I am plotting directly energies. Also, for the strain, which units should be used? Simply distance units of % with respect to the relaxed?

Thank you very much.

Stress is Force acting normal to a surface area per surface area. Therefore, it is the negative gradient of energy per surface, or the energy difference per length along the strain direction per surface, or energy difference per volume difference due to strain. I hope this helps.