[Pw_forum] Praseodymium Pseudopotential(s)
Stefano Fabris
fabris at democritos.it
Tue Aug 31 15:09:54 CEST 2010
Hi Paul (and Trinh Vo),
unfortunately I do not have a specific experience with Pr or Yb, but
you are welcome to take as a starting point the parameters I used for
the Ce PP. In attachment you may find some input files for
pseudopotentials we have generated some years ago by using the
Vanderbilt code (http://www.physics.rutgers.edu/~dhv/uspp/, version
734). I have tested the pseudo on the properties of CeO2-based
materials only. In my experience, semicore states were very important
while adding more projectors to the f channel made little difference.
This may however be very element-dependent. In any case, as noted by
Stefano de Gironcoli, the self-interaction error is a serious issue in
rare-earth materials and the DFT+U approach is one way to cope with it.
Finally, I could also find some material on Pr that was sent to me
many years ago by Paolo Giannozzi. I do not think that it was ever
used, so again, no guarantee, but maybe you can find it useful.
You can refer to me if you have questions that are too specific for
the forum, I will be happy to contribute as far as I can. Hope it helps.
Yours sincerely,
Stefano
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On 27 Aug 2010, at 03:11, w2agz wrote:
> Hi Stefano(s),
>
> Thanks for your feedback. I wouldn't be surprised that praseodymium
> would
> have similar issues as cerium. Ce is [Xe]4f 5d 6s2 and Pr [Xe]4f3
> 6s2,
> and, as I mentioned below, Pr-1237 is the only lanthanide copper oxide
> perovskite that doesn't superconduct. (The Ce copper oxides don't
> form in
> the same perovskite structure).
> In any event, your comment that correlations in these materials are
> very
> cogent, and that employing a LDA+U framework is mandatory.
>
> You mentioned "...posting pseudos on the web"...is it possible for
> QE users
> to submit PPs they've found handy to the QE Wiki? I constructed a PP
> favoring the Cu 3d9 4s2 configuration which I found very useful for
> calculating ground state antiferromagnetic properties of CuO, both as
> tenorite and tetragonal rocksalt. I generated it using the QE PP
> code, and
> could make it available (no guarantees, of course!).
>
> -Paul
>
>
>
> --------------------------------------------------
> From: "Stefano de Gironcoli" <degironc at sissa.it>
> Sent: Thursday, August 26, 2010 12:21 AM
> To: "PWSCF Forum" <pw_forum at pwscf.org>
> Cc: "Stefano Fabris" <fabris at democritos.it>
> Subject: Re: [Pw_forum] Praseodymium Pseudopotential(s)
>
>> Dear Paul,
>> I have no experience with Praseodymium but have been involved in
>> some
>> calculations with Cerium that shares with it the mixed valence
>> nature.
>> Stefano Fabris (here in cc) generated a couple of pseudopotentials
>> that were successfully used in a number of studies. He can send you
>> more info... and possibly post the pseudos on the web...
>> Beware however that in order to obtain even qualitatively sensible
>> results with Ce (and I guess also with Pr) DFT+U or a similarly
>> self-interaction corrected scheme is mandatory.
>> best regards,
>> Stefano de Gironcoli
>>
>>
>> w2agz wrote:
>>> Ciao Tutti (especially Paolo, Mateo etc.),
>>>
>>>
>>>
>>> OK, I've been away for a while, busy with energy issues and trying
>>> to
>>> understand why Alex Mueller may have been on the right track wrt to
>>> explaining why high temperature superconductivity manifests in the
>>> copper
>>> oxide perovskites. PW_FORUM is not the right place to "advertize"
>>> one's
>>> publications, but I owe much to the QE community and its creators
>>> and
>>> contributors. Contact me if you're interested in further info.
>>>
>>>
>>>
>>> The reason for this posting is as follows:
>>>
>>> (1) I'd like to investigate via QE-DFT the "properties" of
>>> several Pr,
>>> alkaline earth-oxide perovskites, and thus need to have an
>>> appropiate Pr
>>> pseudopotential, one that would be compatible with the PP library
>>> of QE.
>>>
>>> (2) Browsing the QE, Vanderbilt, Opium, Haber and Martins sites
>>> (US-PS, NC-PS), I could find "none" that were pregenerated.
>>>
>>> (3) Therefore, I may be "on my own," and would appreciate advice:
>>>
>>> a. Is the community aware of any suitable Pr PPs I could
>>> obtain and
>>> use?
>>>
>>> b. If not, I'd appreciate advice on how to generate my own,
>>> using
>>> either the "famous" ld1.x, or a suitable equivalent
>>>
>>> c. Does anyone know about or use the "Octopus" site
>>> (http://www.tddft.org/programs/octopus)
>>>
>>> (4) Pr is a particular pernicious element ([Xe] 4f3-6s2) .
>>> Simply
>>> put, it can be either 3+ or 4+.or somewhere in between - the 4f
>>> states
>>> are known to hybidize extensively. Studies I did at IBM on the
>>> Pr-1237
>>> system indicated its ground quantum state may be in some sort of
>>> "heavy
>>> fermion" configuration. Think about it. Why is not Pr-1237
>>> superconducting.or even metallic, even though its crystal
>>> structure is
>>> nearly identical to Y-1237? That's the most unsolved mystery of
>>> 20th
>>> century condensed matter physics.next to why the copper oxide
>>> perovskites
>>> are superconducting at all.
>>>
>>>
>>>
>>> Finally, I remind all of the wisdom of David Vanderbilt's remark,
>>> something to the effect, "Pseudopotential generation is a black
>>> art."
>>>
>>>
>>>
>>> Paolo, can you work your magic?
>>>
>>>
>>>
>>> Ciao, -Paul
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
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>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
>>> http://www.democritos.it/mailman/listinfo/pw_forum
>>>
>>
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>
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---
Stefano Fabris
Theory at Elettra group
CNR-IOM DEMOCRITOS Simulation Center and
SISSA - Scuola Internazionale Superiore di Studi Avanzati
email: fabris at democritos.it tel: +39 040 3758-735 fax: -776
www.democritos.it/~fabris
---
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