[Wien] EFG: theory Vs experiment for a case

[Ashwani Kumar]

Thanks everyone for the warm discussion.  I started fresh again with the
STO.
Dear Dr. Laurence, can you share the reference's information.
Yes that's true,  present literatures focuses on the Oxygen vacancy in STO
created due to controlled synthesis parameters (like partial pressure of
oxygen). That's why i tried my calculations for O-vacancy.

thanks,
A. Kumar



On Wed, Dec 19, 2018 at 4:23 PM Lyudmila Dobysheva <lyuka17 at mail.ru> wrote:

> 18.12.2018 22:38, Ashwani Kumar wrote:
> > the assymetry parameter, (Vxx-Vyy)/Vzz,  is zero
> > (wien2k calculation)
>
> I just want to be sure for any occasion: you take the :EFG and :ETA data
> from the scf file?
>
> > STO has
> > cubic lattice so no efg and no assymetry  parameter (for both wien2k and
> > TDPAC) but defect STO structure showed very pure hyperfine interactions
> > with assymetry parameter : 0.52. So i am not having confidence over my
> > wien2k calculation because :
> > 1. i am getting assymetry parameter =0
>
> So, Vxx=Vyy. This really can be due to an artificial choice of supercell.
>
> I am not familiar with TDPAC experiments. What is its experimental error
> for EFG and ETA?
> > 2. Negative EFG which i understood from previous answers that negative
> > sign indicates the rate of decrease of z-component of EF wrt to distance.
>
> I prefer to think about EFG as second derivative of a _scalar_
> potential, than a first derivative of a _vector_ electric field (though
> it's the same value, it is easier for me). Then, negative or positive
> values are the curvature of potential in this direction.
>
> 19.12.2018 12:48, Ashwani Kumar wrote:
>  >> 1.Must do 3x3x3 supercell calculation
>
> To check the idea of Stefaan that EFG is due to asymmetry of Hf
> sublattice (3x2x2): have you calculated without oxygen vacancies? The EFGs?
>
> I'd say that relaxation of atoms is very important for EFG.
>
> Best wishes
> Lyudmila Dobysheva
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