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Hi,

If we apply tensile strain along 'c' axis to a hexagonal lattice, should we relax the out of plane lattice parameter (i.e. 'a') in addition to ionic relaxation?
In some papers, I observed they considered relaxation of lattice 'a' and in other papers, they just relax the atomic coordinates.
1. Which one is more reasonable for electronic and optical properties?
2. What should be the case when we apply bi axial strain along 'a'?

hi
i have almost similar question, rather my question may help you to some extent.

as per my understanding and as per my work, i am applying uniaxial strain (tensile and compression) and studying the bandgap variation. I was suggested by a senior that we should not relax the cell, as it may tend to come back to the original position before applying strain.
So, i did not relax the cell but straight away computed band structure in that condition, that is a static run.
Using the same concept, i applied optics tags and computed optical properties, means again static run. the only major change of input file is KPOINTS files in both cases, and optics tags.

Now, if i understood correctly, within the single static run also the atoms will move till EDIFF is satisfied. Right? then can we consider or assign the optical property changes corresponding to the atomic movements, in different strains applied?
Can anyone help me in further opinion or correct me if i am wrong?

Regards