[Wien] 'NN' - overlapping spheres during the volume optimization

[Stefaan Cottenier]

> I am using the PBE-GGA functional. According to the
> http://prb.aps.org/abstract/PRB/v79/i8/e085104 paper, it is indeed the
> best choice for Fe. However, LDA seems to be the best for Ge. Well, it
> looks like that the Fe-Ge system is not very convenient for this kind of
> optimizations.

That's perhaps too negative as conclusion. Even though you might not be 
able to predict the absolute volume with 1% accuracy, relative trends 
should be much better, more or less independent of the functional (e.g. 
volume change upon the introduction of a given amount of vacancies).

STefaan