[Pw_forum] Example07

[Paolo Giannozzi]

On Feb 14, 2007, at 7:28 , Paul M. Grant wrote:

> The README file for example07 contains the rather cryptic remark  
> that, “…the k-point grids used here are NOT dense enough for a  
> serious calculation!”.  Yet the lambda that results ranges from  
> 0.34 – 0.34 depending on broadening (the experimental value for  
> lambda for Al is approximately 0.44).  Not too bad.  Increasing 16  
> 16 16 and 8 8 8 to a 32 32 32 and a 16 16 16 MP grid, respectively,  
> yields lambdas in the range 0.34 – 0.39.  How big do I have to go?   
> -Paul

it depends on what you want to calculate and how accurately.
If you want just a rough estimate of the electron-phonon
interaction coefficient lanbda, you may not need a dense
grid, but in order to get an accurate number for superconducting
T_c, you need it. Al is not especially nasty from this point of view,
there are worse cases

Paolo
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Paolo Giannozzi, Democritos and University of Udine, Italy