[Pw_forum] about nonlinear core-correction for pseudopotentials

[Paolo Giannozzi]

On Wednesday 28 June 2006 17:34, sun jason wrote:

> 1) on the pwscf website, why all the ultrasoft pseudopotentials with GGA
> for boron are all include nonlinear core-correction, while this correction
> is not considered for carbon and nitrogen ? Is that means this correction
> is very important for boron but not for carbon and nitrogen ?

typically the core correction is more important for atoms with few valence
electrons

> 2) Is there any relation between PBE exchange-correlation ? I find the LDA
> norm-conserving PPs are not include NLCC.

no direct relationship, but gradient-corrected functionals tend to be
ill-behaved when rho(r) => 0, i.e. at large r but also at small r for
pseudopotentials. This may lead to instabilities in the pseudopotential
generation procedure, or to pseudopotentials with an unpleasant 
"spike"  at r=>0.  With the core correction there is no such problem.

Paolo
-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
Piazza dei Cavalieri 7      I-56126 Pisa, Italy