[Pw_forum] Crystal Structures in QE

Cameron Foss cjfoss at umass.edu
Sat Aug 30 09:33:32 CEST 2014

Hello all,

I have some questions about how structures are specified in QE:

Are the K_POINTS in the scf calculation for pw.x responsible for specifying
some relevant shape? (eg 4 4 4 or 8 8 8 = bulk material,   and 4 4 1 or 8 8
2 = thin film/2D structure)

To put this in context, I am trying to measure the effects of Strain on
phonons and crystal structure of thin films of silicon stretched over some
SiGe Alloy or Ge substrate. The result being a stretched layer of silicon
over the substrate which is stretched in the 100 and 010 directions, and
negligibly compressed in the 001 direction. It is important that the
structure does not relax at all in the calculation for this would give
misleading results.

Thus far i have been using K_POINTS such as 4 4 4 or 8 8 8, and am curious
to know if these K_POINTS are meant for specifying bulk materials, and if I
should change to something more like 4 4 1 or 8 8 2 for thin filmed

Best Regards,
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