[Q-e-developers] Proposed code additions for 2D systems

[Richard Andrew]

Dear QE team,

You requested we send any code additions we may have.   I work in 2D systems and I noticed most DFT codes have no way for you to relax the 2D cell shape while keeping the area constant.  The cell_dofree='shape' option in QE relaxes all degrees of freedom for the cell shape at constant volume which for 2D systems means also changing the vacuum layer.  I have modified the cell_base.f90 module to include a cell_dofree='2Dshape' option which will relax the in-plane (xy plane) cell shape while keeping the area (therefore the vacuum layer) constant.  This also required a change in the deviatoric.f90 code in the flib.  Please find attached these modified files for your consideration.  All modifications are marked between '! RICHARD' comment lines.

I also included in cell_base.f90 a cell_dofree='2Dxy' option where the xy  plane is truly free as you had suggested in your code comment for cell_dofree='xy'.

Regards,

Richard Charles Andrew


Postgraduate Student
Physics Department
University of Pretoria
South Africa
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