[Wien] Large difference in calculated and experimental EFG

[Peter Blaha]

Most importantly: You talked about a 2x2x2 supercell ???

We don't know how big your original cell was, but a 16 atome cell with 1 
T is not an impurity as measured in PAC.
How many atoms are in this supercell ???

You must probably increase the supercell size and check convergence of 
the EFG.

On 3/18/19 1:15 PM, Stefaan Cottenier wrote:
> If the goal is to have a EFG that is a predictive as possible for 
> experiment, then it is advised to take the experimental cell parameters 
> (but with position optimization).
> 
> If that EFG does not agree with experiment, then this is a trigger to 
> search further. There can be many reasons (assuming both the experiment 
> and the calculation are correctly done):
> 
>   * You have an unusually sensitive case, where small details that
>     usually do not matter do affect the EFG
>   * The effect of temperature might be unusually large (your calculation
>     is at 0 K)
>   * Maybe the Ta atom is associated with a defect (vacancy, oxygen,…)
>     and the experiment measures that complex.
>   * …
> 
> Stefaan
> 
> *From:*Wien <wien-bounces at zeus.theochem.tuwien.ac.at> *On Behalf Of 
> *Ramsewak Kashyap
> *Sent:* Monday, March 18, 2019 12:41 PM
> *To:* A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at>
> *Subject:* Re: [Wien] Large difference in calculated and experimental EFG
> 
> atomic positions  optimization means force relaxation.. I have did that. 
> but I am asking about cell parameter optimization. Is it necessary for 
> .cif file getting form COD??
> 
> Thanks
> 
> On Mon, Mar 18, 2019 at 4:55 PM Stefaan Cottenier 
> <Stefaan.Cottenier at ugent.be <mailto:Stefaan.Cottenier at ugent.be>> wrote:
> 
>     Yes, optimization of the atomic positions is absolutely necessary to
>     have a meaningful value for Vzz and eta in a supercell.
> 
>     Stefaan
> 
>     *From:*Wien <wien-bounces at zeus.theochem.tuwien.ac.at
>     <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>> *On Behalf Of
>     *Ramsewak Kashyap
>     *Sent:* Monday, March 18, 2019 12:23 PM
>     *To:* A Mailing list for WIEN2k users
>     <wien at zeus.theochem.tuwien.ac.at
>     <mailto:wien at zeus.theochem.tuwien.ac.at>>
>     *Subject:* [Wien] Large difference in calculated and experimental EFG
> 
>     Hi Wien2k users,
> 
>     I am doing EFG calculation for TiNi monoclinic phase, but I am
>     getting large difference in Calculated and measured value, I have
>     taken parameters from COD, then make 2x2x2 supercell and replace one
>     Ti with Ta atom... is structural optimization is necessary??  and
>     eta value was also quite large as compare to measured value.
> 
>     -- 
> 
>     Ramsewak Kashyap
>     Saha Institute of Nuclear Physics
>     9473811023
> 
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> 
> -- 
> 
> Ramsewak Kashyap
> Saha Institute of Nuclear Physics
> 9473811023
> 
> 
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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