[Wien] EFG: theory Vs experiment for a case

[Peter Blaha]

The presence of an EFG and of a non-zero eta is first of all a symmetry 
property.

If you get in exp eta=0.5, but in theory eta=0.0 (by symmetry ?), it 
simply means that the Hf impurity in PAC is not at the same position or 
does not have the same environment than the Hf in your simulations.

In other words: you seem to have placed the Hf on a "high symmetry" 
site, while in experiment it is sitting somewhere else.

Depending on the treatment of the sample (tempering after Hf 
implantation) this ion may sit on various places in the cell.

You did not say anything how you simulate the impurity. Why a 3x2x2 
supercell (for a cubic cell ???) ? Where is it sitting, did you fully 
relax the positions, ... ??

PS: Please use the EFG/eta from the scf file.
The x lapw2 -efg is just an option for interpretation and analysis, from 
which orbitals the main components of the EFG originates.

Am 18.12.2018 um 19:38 schrieb Ashwani Kumar:
> hi,
>     thanks for reply. the assymetry parameter, (Vxx-Vyy)/Vzz,  is zero 
> (wien2k calculation) whereas i got 0.52 from TDPAC (Time dependent 
> perturbed angular correlation) spectroscopy for a SrTiO3 (STO) defect 
> structure. EFG component is -1.63 x10^21 V/m2 (wien2k, lapw2 -efg) and i 
> obtained 1.69 x 10^21 V/m2 (calculated from TDPAC results). 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
> 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.
> 
> Am i missing something?,
> Calculation parameters are :Supercell (3x2x2) STO with doped Hf atom, 
> PBE, KGEN:200, rkmax: 7.0,
> 
> thanks,
> A. Kumar
> 
> On Fri, Dec 14, 2018 at 11:02 PM Ashwani Kumar <ashwani.ism at gmail.com 
> <mailto:ashwani.ism at gmail.com>> wrote:
> 
>     Hi,
>        i have calculated EFG  the defect structure of crystalline system
>     from experimental data from PAC spectroscopy. Then using WIEN2K
>     (crystal structure--> supercell--> defect introduced), EFG is
>     calculated.
>     Exper. Calculated : 1.69 x 10^21 V/m2 whereas wien2k calculation:
>     -1.66 x 10^21 V/m2 (crude value still have to do lapw2 -efg) on
>     probe atom. Wien2k calculation shows negative value. is there any
>     significance of the negative sign.
> 
>     thanks,
>     A. Kumar
> 
> 
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-- 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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