[Pw_forum] Crystal Structures in QE

[Paolo Giannozzi]

On Sat, 2014-08-30 at 03:33 -0400, Cameron Foss wrote:

> 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)

I would say that it is the other way round: the shape of the cell
determines the k-point grid

P.

> 
> 
> 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 structures?
> 
> 
> Best Regards,
> Cameron
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