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[verstraete@pcpm.ucl.ac.be]

Hello Paul,

I have a bit of experience with abinit and FHI98PP, so here goes: I think 
your problem is with the generation of the pseudopotential. A rchrg of 10 
bohr is huge! Much bigger than the atom itself. For example, Cs is 
already a very stout atom, and it only needs a rnlc of 3.50.

You should (rule of thump) set rchrg slightly smaller than the radius
where the core and valence charges are equal (ie not where the core is 0).
The other two variables are just flags. Setting them to 1.0 is fine.

Which element do you use a NLCC for? I just looked at the default fhi98PP 
input files for Ga and As (made by Martin Fuchs, and usually very good), 
and neither uses a NLCC... There is the possibility of adding the d 
semicore electrons (file ~fhi98PP/bin/Elements/TM/31-Ga-3d:tm.ini).
If I remember correctly, this was Martin's recommendation for Ga, because 
there is a substantial overlap of the 3d with the 4s and 4p.

Matthieu


On Thu, 27 Mar 2003, Paul Tangney wrote:

> Dear ABINITioners,
> 
> Has anybody encountered problems with nonlinear core corrections
> in ABINIT ?
> 
> I am using pseudopotentials that I generated with the Fritz-Haber
> code FHI98PP. The total energy that I get disagrees slightly with
> the results using the PARATEC plane wave code. Differences are of
> the order of 1 or 2 mRyd. (and about 4 GPa in the stress).
> The system is GaAs - I haven't checked other systems, but if
> I make PPs without core-corrections I can get both codes to agree to a
> high precision.
> 
> I am a new user of ABINIT (and also PARATEC) and so the problem
> might be something very simple, but before I get my hands dirty
> by delving into the source I thought I should ask to try to
> figure out whether the problem is with me, PARATEC, or ABINIT.
> In particular, I'm a little confused about the input variables
> "rchrg","fchrg" and "qchrg" that are on the 4th line of the
> PP files. I have set rchrg to 10.0 where the core charge is zero
> and I have values of 1.0 for both fchrg and qchrg but I don't
> know if this is correct.
> 
> I would be very grateful for any help you could give me.
> 
> Best regards,
> 
> 
> Paul
> 
> 
> 
> 

-- 
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Matthieu Verstraete               mailto:verstraete@pcpm.ucl.ac.be 
PCPM, Boltzmann, pl. Croix du Sud, 1            tel: 010/ 47 86 81
B-1348 Louvain-la-Neuve  Belgium                fax: 010/ 47 34 52