[Pw_forum] Praseodymium Pseudopotential(s)

[w2agz]

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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