[Pw_forum] optimization and pseudo potentials

[Giuseppe Mattioli]

Dear James
I did not know that Davide put his own PP library online... Thanks for  
sharing!
As far as I can see, there seems to be no intrinsic reason because  
these pseudopotentials should behave so badly in vc-relax (or even  
relax) calculations. But they are Troullier-Martins norm conserving  
pseudopotentials (tm-gipaw), and they may be quite harder than PAW  
pseudopotentials with non-linear core corrections (n-kjpaw). Have you  
tried to check the convergence for ecutwfc?
HTH
Giuseppe

Giuseppe Mattioli
ISM-CNR
Italy

Quoting James Mao <xjamesmao at gmail.com>:

> Hi Giuseppe,
>
> The PPs part in my input is:
>
> ATOMIC_SPECIES
>  Al 26.98 Al.pbe-tm-gipaw-dc.UPF
>  O  16.00  O.pbe-tm-new-gipaw-dc.UPF
>  P  30.97  P.pbe-tm-new-gipaw-dc.UPF
>
> I got these PP files from here:
>
> https://sites.google.com/site/dceresoli/pseudopotentials
>
> I always use them for GIPAW calculations and they works fine. Never  
> realized they might not
> be suitable for other types of calculations like optimization. So I  
> think this is a good chance
> for me to get educated. lol
>
> Thanks again!
>
> Best,
> James
>
>
> -----Original Message-----
> From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org]  
> On Behalf Of Giuseppe Mattioli
> Sent: Tuesday, January 28, 2014 2:15 PM
> To: pw_forum at pwscf.org
> Subject: Re: [Pw_forum] optimization and pseudo potentials
>
>
> Dear James
> Hard to help you without seeing the PP files or their generation input files.
> Where did you find the PPs? I do not spot them in the online library...
> Yours
> Giuseppe
>
> Giuseppe Mattioli
> ISM-CNR
> Italy
>
> Quoting James Mao <xjamesmao at gmail.com>:
>
>> Dear users,
>>
>>
>>
>> I am trying to calculate NMR chemical shifts by GIPAW for a crystal
>> (with atoms Al, P, O). The pps I used
>>
>> with GIPAW are "pbe-tm-gipaw-dc" sets. I did get reasonable results.
>>
>>
>>
>> For a second step I tried to optimize the structure. I noticed if I
>> still used the gipaw pps, the optimization
>>
>> process is completely wrong. In vc-relax calculations the cell volume
>> keeps shrinking to 67% of original
>>
>> volume (which is from experimental structure). While I changed the pps
>> to "pbe-n-kjpaw" set, vc-relax
>>
>> gave reasonable results.
>>
>>
>>
>> I would be very thankful if someone can explain a little bit for me
>> what kind of pps are not suitable for
>>
>> optimization so in future I can avoid similar mistake? Any helps will
>> be greatly appreciated.
>>
>>
>>
>> Best regards,
>>
>> James Mao
>>
>>
>>
>> Postdoc associate
>>
>> Department of Chemistry,
>>
>> University of Pittsburgh
>
>
> --
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>     Giuseppe Mattioli
>     CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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-- 
********************************************************
- Article premier - Les hommes naissent et demeurent
libres et ègaux en droits. Les distinctions sociales
ne peuvent être fondèes que sur l'utilitè commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et
imprescriptibles de l'homme. Ces droits sont la libertè,
la propriètè, la sùretè et la rèsistance à l'oppression.
********************************************************

    Giuseppe Mattioli
    CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
    v. Salaria Km 29,300 - C.P. 10
    I 00015 - Monterotondo Stazione (RM)
    Tel + 39 06 90672836 - Fax +39 06 90672316
    E-mail: <giuseppe.mattioli at ism.cnr.it>