[Pw_forum] Re: stress in CP and FFT grids

[Konstantin Kudin]

 Hi Axel!

> what kind of cutoffs are you using? 
> does your system expand or shrink? and how much?

 Ordinarily, I would use the cutoff of 25 Ryd, however, for the
constant pressure I was using 30 Ryd with the modified kinetic energy
functional 
[ecutwfc = 30.0, ecfixed = 25.0, qcutz = 25.0, q2sigma = 3.0]

 I started with Z=22 A, the grid was:
   Array leading dimensions ( nr1x, nr2x, nr3x )   =     90    90   192
   Array leading dimensions ( nr1x, nr2x, nr3x )   =     72    72   150
   Array leading dimensions ( nr1x, nr2x, nr3x )   =     24    24    24

 It settled around Z=23 A (I optimized only Z), and if I restart a
fresh calculation with all the same parameters, i get:

   Array leading dimensions ( nr1x, nr2x, nr3x )   =     90    90   200
   Array leading dimensions ( nr1x, nr2x, nr3x )   =     72    72   160
   Array leading dimensions ( nr1x, nr2x, nr3x )   =     24    24    24
 
 So the change in the grid is pretty much unaccounted for by the
constant pressure simulation. I guess I could force the Z=23A run to
use the same grid as before, however, that is not so clean.

 Thanks!
 Kostya

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