[Pw_forum] About Pseudo-Potential generation

[Paolo Giannozzi]

On Jan 23, 2007, at 12:16 , Lawrence Lee wrote:

> (1) Comparing Rabe-Rappe-Kaxiras-Joannopoulos and Troullier-Martin  
> pseudization, it seems that the former is simpler. But actually  
> which one
> is better?

my impression is that RRKJ yields softer potentials than TM, but TM
always works, RRKJ often fails to produce a potential

> (2)
> What's the difference between using one channel as the local PP
> and pseudizing the all electron potential.

one channel less to be treated as nonlocal

> (3)
> Sometimes, one will use fractional occupation such as [Ne]3s1.5 for  
> Mg.
> Why's that?

computational convenience, more freedom in choosing the reference
configuration

> (4)
> If I want to do high pressure calculation later, does it mean that  
> I must use
> a small core radius.

preferrably, yes.

The notes on pseudopotential generation that come with the
documentation of the atomic code contain several answers
to frequent questions on pseudopotentials

Paolo
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Paolo Giannozzi, Democritos and University of Udine, Italy