[Pw_forum] pseudopotential for studying high-pressure elements

[Nichols A. Romero]

Hi,

I am interesting in doing DFT calculations of some elements at
high-pressure, e.g. carbon.

Some pseudopotential (PP) generating schemes achieve superior total
energy convergence versus planewave cutoff  but at the "cost" of
increasing r_c.

The paper by Troullier and J. L. Martins PRB 43, 1993 (1991) states
that if one matches the transferrabiliy of the pseudopotentials (I
assuming through the logarithmic derivatives) then the radii used in
the TM scheme are double that in the HSC scheme. The result is that
the PP generated in the TM scheme is softer than the HSC.

My question is: 
Will the PP give meaning results once the atomic seperation is less
than r_c. In general, I would think not. So the next question is that
for a fixed r_c what PP will be softess: TM, RRKJ, Ultrasoft-PP, etc.?

I would appreciate comments and any relevant citations that I may have
overlooked.

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