[CP2K-user] [CP2K:16416] Wrong Cell Parameters When Optimizing BaTiO3 Unit Cell

[fabia...@gmail.com]

Dear Rylin,

You have no correlation in your XC functional. I have never used the 
Cohen-Wu functional but from skimming the paper I think you should add the 
pbe correlation to your input file:
&XC_FUNCTIONAL
    &GGA_X_WC
    &END
    &GGA_C_PBE
    &END       
&END XC_FUNCTIONAL

Please make sure to double check this!

Cheers,
Fabian
On Wednesday, 22 December 2021 at 13:45:02 UTC+1 ruilin... at gmail.com wrote:

> Dear Prof.  Kühne
>
> Thank you for your reply!
> I modified my code by using a diagonalization method with a 
> 4x4x4 Monkhorst-Pack k-point mesh. It indeed makes sense, however, there is 
> still a big gap between the calculated cell parameters and the experimental 
> results.
> While using Cohen-Wu functional, the length of a and b axis seems 
> acceptable, however, the length of c axis is about 4.6 angstroms. I think a 
> difference of 0.6 angstroms is a little big. I also tried normal PBE 
> functional. the calculated length of c axis is about 4.2 angstroms, still 
> has a difference of about 0.2 angstrom from the experimental results. How 
> can I improve my codes?
> Looking forward to your reply!
>
> Best regards,
> Rylin Mao
> 在2021年12月22日星期三 UTC+8 00:40:36<tkuehne> 写道：
>
>> Try to use at least a 4x4x4 k-point mesh. 
>>
>> Best, 
>> Thomas Kühne
>>
>> Am 21.12.2021 um 16:46 schrieb 毛瑞麟 <ruilin... at gmail.com>:
>>
>> Dear CP2K Users:
>>         I faced some problems while optimizing Tetragona BaTiO3 unit 
>> cell.  I use direct cell optimization method, with Cohen-Wu Exchange 
>> correlation functionals.  As described in literature, Cohen-Wu functional 
>> is the best functional which can be used in ferroelctric systems. However, 
>> the cell parameters after optimization EXTREMELY (a=b=4.30 angstroms, 
>> c=5.59 angstroms) diverge from  cell parameters measured by experiments 
>> (a=b=3.99 angstroms, c=4.04 angstroms). All electron steps converge 
>> normally. 
>>         I also tried normal PBE functional and PBEsol functional, the 
>> cell parameters seemed far away from what is normal. 
>>         So can anyone tell me what's wrong with my codes or how can I 
>> modify my code?
>> Best regards
>>
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>> .
>> <0.out><1.inp><3-1.cell>
>>
>>
>>
>>
>> ==============================
>> Thomas D. Kühne
>> Dynamics of Condensed Matter
>> Chair of Theoretical Chemistry
>> University of Paderborn
>> Warburger Str. 100
>> D-33098 Paderborn
>> Germany
>> thomas... at upb.de
>> +49/(0)5251/60-5726 <+49%205251%20605726>
>>
>>

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