What is the proper approach to optimize a 3D cubic crystal structure after applying Biaxial Strain in QE ?
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$\begingroup$ Welcome to the site. The 'cell_dofree' tag might be what you are looking for - it has settings for epitaxial strain, e.g. 'epitaxial_ab' (depending on the orientation of your crystal; I assume you'd like to simulate epitaxial strain) $\endgroup$– manju9Commented Nov 22 at 12:17
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$\begingroup$ Thank you for your response, actually not Epitaxial but Biaxial strain(for x and y axis), and yes for the cell_dofree parameter, I used it and fixed the 'z', but it just that the results I got are different from the ones that I was expecting, If anyone worked on the same approach, many thanks. $\endgroup$– JiaCommented Nov 22 at 13:20
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$\begingroup$ If you want to use cell_dofree to lock specific parts as desired, you need to appropriately modify the source code in Modules/cell_base.f90 and then recompile program. $\endgroup$– user23915364Commented Nov 24 at 9:51
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$\begingroup$ I believe that these are similar - biaxial means you stretch/compress along two lattice directions, say a- and b-axis and the last remaining one expands/contracts according to e.g. the Poisson ratio. In this case you could calculate the new in-plane lattice constants from the strain and relax the orthogonal direction to account for lattice relaxation. Is this what you wish to do? $\endgroup$– manju9Commented Nov 25 at 9:43
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$\begingroup$ Thank you for the for the last two responses. User23915364, I don't really get the Modules part, I am somehow new to QE work and searched a bit about the Modules part and don't get it yet. And Manju9, yes that is it, thank you the issue is that when calculating the band gap it doesn't give the value expected, so I was wondering if I was on the right way, so still looking for a solution for that, many thanks $\endgroup$– JiaCommented Nov 26 at 11:00
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