Including inner shell electrons in GPW calculations

[Rustam]

Hi guys,

I need to include inner-shell electrons of Mg into my GPW calculations. 
That is the total number of electrons on magnesium must be 10, not just 2 
valence 3s electrons.

This can be readily achieved using by using the following pseudopotential

&KIND Mg

  BASIS_SET DZVP-GTH

  POTENTIAL GTH-BLYP # 2s2 2p6 3s2 configuration

&END


instead of typical


&KIND Mg

  BASIS_SET DZVP-GTH

  POTENTIAL GTH-BLYP-q2 # 3s2 

&END

I figured (by trial and error) that including inner electrons requires 
significantly higher CUTOFF setting. The attached plot shows energy 
dependence on the cell size of MgH2.

A. 2-electron calculations are fine with 1000 Ry cutoff
b. 10-electron calculations produce awful results unless the cutoff is 
above 8000 Ry.

QUESTION: Is it really necessary to use such a high cutoff to get smooth 
curves? Or are there any other settings one can tweak to get accurate 
results with lower (i.e. cheaper) cutoff?

Thanks!
Rustam

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