Re: [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  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
> --
> Physics-Techn.Institute,
> Udmurt Federal Research Center, Ural Br. of Rus.Ac.Sci.
> 426000 Izhevsk Kirov str. 132
> Russia
> ---
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>
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Re: [Wien] EFG: theory Vs experiment for a case

[Stefaan Cottenier]

> I don't know if one can trust eta from the PAC results ?

In principle there is no objection. If it is a sufficiently clean experiment 
(good statistics, not too many different sites, sufficiently strong EFGs,...) 
then TDPAC can get eta with an error bar better than 0.1.

> > To what % agreemnet wrt experimental efg data, efg values from
> > theoretical calculation can be accepted.

Have a look at http://dx.doi.org/10.1021/acs.jpcc.6b06127 . The literature 
history is in this sentence on page 2:

"A rule of thumb of 10−20% is sometimes quoted [18,19,21,24] yet the origin of 
this number is
unclear and certainly not based on rigorous testing."

and the detailed analysis for the error bar on the EFG for 111Cd in hcp-Cd is 
in the section 'error budget' on page 4. The resulting error bars are listed in 
the last column of Tab. 1. 

Stefaan
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Re: [Wien] EFG: theory Vs experiment for a case

[Laurence Marks]

I remain shocked that the majority of the recent STO literature has ignored
the older, more careful literature. The dominant point defect is the
valence neutral divacancy SrO, particularly under oxidizing conditions. I
strongly suggest you research the papers with real measurements, not those
with speculations!

_
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu

On Wed, Dec 19, 2018, 2:47 AM Ashwani Kumar   System under study is SrTiO3 doped with
> Hf-181 tdpac probe for TDPAC spectroscopy by thermal equillibriation method
> (1250 C for >12 hours). the doping is substitutional as Hf(IV) and Ti(IV)
> has nearby ionic radius and same oxidation state. Bulk STO shows no efg, no
> assymetry parameter as STO is cubic lattice and Hf/Ti present at octahedral
> symmetry but in another synthetic procedure where synthesis parameters can
> be controlled shows STO with probe showing very pure HFI. From literature,
> STO is known to have oxygen vacancies depending on synthesis route.
>Calculation: STO structure is optimized and
> minimized. Created supercell 3x2x2 as it allows me to use 5 processor with
> 8 gb ram (with 3x3x3, calc. restricted to only 2 processors due to RAM
> limitation. So long scf run time. i will try now) . Problem of breaking
> symmetry did not strike me at the time of calculation. Replaced one Ti by
> Hf. Then supercell calculation was done for oxygen vacancies in first
> cordination and fourth nearest neighbour cordination. The efg matched for
> the later case (oxygen vacancy at fourth nearest neighbour) but not
> assymetry parameter. Minimization of forces on supercell was not done ( i
> thought basic lattice unit was already optimized).
>  What i understood from previous replies of this thread is 1.Must
> do 3x3x3 supercell calculation, 2. Electron electron correlation can also
> be included for improvement of calculation, 3. Need to check calculation
> with reduced RMT of Sr and Ti.
>
> To what % agreemnet wrt experimental efg data, efg values from theoretical
> calculation can be accepted.
> Thanks Dr. Cottenier for the suggestion, i had already subscribed to HF
> course A (ID: iak). I will subscribe to Course B after finishing course A.
>
> Thanks,
> A. Kumar
>
>
> On Wed, Dec 19, 2018 at 12:08 AM Ashwani Kumar 
> wrote:
>
>> 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 
>> 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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Re: [Wien] EFG: theory Vs experiment for a case

[pieper]

As an addendum to previous comments by the experts I strongly recommend 
to always ask (and answer) yourself the question:
what symmetries does the experimental result imply, and what symmetries 
are present in my model?


You state that samples prepared in a precedure 'where synthetic 
parameters can be controlled' (whatever that means) 'shows STO with 
probe showing very pure HFI'. I take it that TDPACS finds Hf in a unique 
environment. All of the spectra is accounted for by a single value 
abs(V_zz)=1.69e21 v/m^2, eta=0.52? No (sizeable) broadening, no other 
lines from different EFG's?


In that case:

1) Whatever model you set up in case.struct, your Hf-site MUST NOT have 
a threefold (or higher) rotation symmetry in its point symmetry group 
(check outputs of structure initialzation programs).


2) Your structure (with your defect of the day) should have a 
significantly lower total energy than other possibilities - otherwise a 
superposition of the corresponding spectra is expected.


Up to now your calculations without neighboring oxygen defects seem to 
be useless because you did not take into account the first point. With 
respect to the second point I am very dubious about your calculations 
assuming oxygen defects in some neighborhood. Some Hf-vacancy pair may 
have a calculated EFG resembling the experimental one. But in an 
unrelaxed structure this is meaningless. And even if you insist to take 
something like that serious, you will have to come up with a really good 
reason why that special defect structure is the only one present in your 
sample!


Looking at your result that the artificial V_zz from your unrelaxed 
3x2x2 supercell already has the same size as the experimental one I 
strongly suspect that you will get a pretty good simulation of the 
experimental result by some very small rearrangement of atoms in the 
nearest, at most the next neighbor shell - WITHOUT oxygen vacany. Put Hf 
on a Ti-site and really DO a relaxation. Start it from a structure with 
appropriate (low) point symmetry at Hf. (shift some neighboring atom(s) 
a tiny bit out of symmetry in some plausible direction).


And remember, EFG is short range - from my experience even a 2x2x2 
supercell may give you a good idea what happens.



---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 19.12.2018 09:48, schrieb Ashwani Kumar:

System under study is SrTiO3 doped with
Hf-181 tdpac probe for TDPAC spectroscopy by thermal equillibriation
method (1250 C for >12 hours). the doping is substitutional as Hf(IV)
and Ti(IV) has nearby ionic radius and same oxidation state. Bulk STO
shows no efg, no assymetry parameter as STO is cubic lattice and Hf/Ti
present at octahedral symmetry but in another synthetic procedure
where synthesis parameters can be controlled shows STO with probe
showing very pure HFI. From literature, STO is known to have oxygen
vacancies depending on synthesis route.
   Calculation: STO structure is optimized and
minimized. Created supercell 3x2x2 as it allows me to use 5 processor
with 8 gb ram (with 3x3x3, calc. restricted to only 2 processors due
to RAM limitation. So long scf run time. i will try now) . Problem of
breaking symmetry did not strike me at the time of calculation.
Replaced one Ti by Hf. Then supercell calculation was done for oxygen
vacancies in first cordination and fourth nearest neighbour
cordination. The efg matched for the later case (oxygen vacancy at
fourth nearest neighbour) but not assymetry parameter. Minimization of
forces on supercell was not done ( i thought basic lattice unit was
already optimized).

 What i understood from previous replies of this thread is
1.Must do 3x3x3 supercell calculation, 2. Electron electron
correlation can also be included for improvement of calculation, 3.
Need to check calculation with reduced RMT of Sr and Ti.

To what % agreemnet wrt experimental efg data, efg values from
theoretical calculation can be accepted.
Thanks Dr. Cottenier for the suggestion, i had already subscribed to
HF course A (ID: iak). I will subscribe to Course B after finishing
course A.

Thanks,

A. Kumar

On Wed, Dec 19, 2018 at 12:08 AM Ashwani Kumar 
wrote:


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 

Re: [Wien] EFG: theory Vs experiment for a case

[Ashwani Kumar]

 System under study is SrTiO3 doped with Hf-181
tdpac probe for TDPAC spectroscopy by thermal equillibriation method (1250
C for >12 hours). the doping is substitutional as Hf(IV) and Ti(IV) has
nearby ionic radius and same oxidation state. Bulk STO shows no efg, no
assymetry parameter as STO is cubic lattice and Hf/Ti present at octahedral
symmetry but in another synthetic procedure where synthesis parameters can
be controlled shows STO with probe showing very pure HFI. From literature,
STO is known to have oxygen vacancies depending on synthesis route.
   Calculation: STO structure is optimized and
minimized. Created supercell 3x2x2 as it allows me to use 5 processor with
8 gb ram (with 3x3x3, calc. restricted to only 2 processors due to RAM
limitation. So long scf run time. i will try now) . Problem of breaking
symmetry did not strike me at the time of calculation. Replaced one Ti by
Hf. Then supercell calculation was done for oxygen vacancies in first
cordination and fourth nearest neighbour cordination. The efg matched for
the later case (oxygen vacancy at fourth nearest neighbour) but not
assymetry parameter. Minimization of forces on supercell was not done ( i
thought basic lattice unit was already optimized).
 What i understood from previous replies of this thread is 1.Must
do 3x3x3 supercell calculation, 2. Electron electron correlation can also
be included for improvement of calculation, 3. Need to check calculation
with reduced RMT of Sr and Ti.

To what % agreemnet wrt experimental efg data, efg values from theoretical
calculation can be accepted.
Thanks Dr. Cottenier for the suggestion, i had already subscribed to HF
course A (ID: iak). I will subscribe to Course B after finishing course A.

Thanks,
A. Kumar


On Wed, Dec 19, 2018 at 12:08 AM Ashwani Kumar 
wrote:

> 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 
> 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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Re: [Wien] EFG: theory Vs experiment for a case

[Stefaan Cottenier]

In addition to what Peter said:

The small EFG you get is a supercell effect. An isolated Hf-impurity on a 
Sr-site (which has a cubic point group, hence zero EFG) would have zero EFG 
too. But by using a tetragonal supercell (3x3x2) your break that cubic 
symmetry. The tetragonal sublattice of Hf atoms generates a non-zero EFG at the 
Hf-site. If you would use a more expensive a 3x3x3 supercell, the EFG on the 
Hf-impurity would be zero by symmetry again.

Such a large asymmetry parameter must be due to a serious (local) distortion. 
Perhaps there is another defect (vacancy, interstitial,…) sitting next to Hf?

And why do you call the negative EFG a reason of no confidence? As I told 
before, the TDPAC experiment measures the absolute value of Vzz only. The EFG 
in experiment might well be negative, but your experiment is not sensitive to 
the sign.

Bottom line: use all indications you have from experiment to build local 
environments for Hf (preferably in a cubic supercell), compute their EFG, and 
compare the absolute values and eta with experiment. When there is a match 
(within 0.5 to 1.0 1e21 V/m2), that local environment is a serious candidate to 
represent the experimental situation.

If you want to learn more about hyperfine interactions (physical background and 
experimental methods), visit this online course: 
www.hyperfinecourse.org<http://www.hyperfinecourse.org> (selfpaced study at any 
time, the next supervised edition starts in February 2019).

Stefaan

From: Wien  On Behalf Of Ashwani Kumar
Sent: Tuesday, December 18, 2018 7:39 PM
To: wien 
Subject: Re: [Wien] EFG: theory Vs experiment for a case

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 
mailto:ashwani@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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Re: [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 > 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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--
--
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: bl...@theochem.tuwien.ac.atWIEN2k: http://www.wien2k.at
WWW: 
http://www.imc.tuwien.ac.at/tc_blaha- 


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Re: [Wien] EFG: theory Vs experiment for a case

[Laurence Marks]

With STO PBE is too covalent. For many properties you need to use either
-eece (my preference), +U or a full hybrid. In addition the default RMT for
Sr in STO is normally too large, something like 2.05 is better.

N.B., be careful not to have the Ti RMT too large as then the tails of the
O 2p enter the Ti RMT and give you pseudo-d's.

On Tue, Dec 18, 2018 at 12:38 PM Ashwani Kumar 
wrote:

> 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 
> 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
>>
>

-- 
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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Re: [Wien] EFG: theory Vs experiment for a case

[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 
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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Re: [Wien] EFG: theory Vs experiment for a case

[Lyudmila Dobysheva]

> From: Ashwani Kumar Friday, December 14, 2018 6:33
> 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

> Friday, December 14 2018, 21:40 +04:00 from Stefaan Cottenier 
> :
> Most EFG experiments measure the absolute value only, hence you usually do 
> not know the experimental sign.
> The meaning of the sign is the same as for any derivative: a negative Vzz 
> means that d Ez/dz is negative: the value of the z-component of the electric 
> field becomes * smaller *
>  if you go along the positive z-axis.

An addition to what Stefaan said:
According to Laplas equation Vxx+Vyy+Vzz=0, EFG is the biggest among them, and 
it is chosen as Vzz. So it is not z-axis of global or local coordinate system, 
it is the biggest among the three values. Vxx is the smallest one. Now imagine 
that in our system Vxx is almost zero. Then Vzz= - Vyy, they are almost equal. 
Now, small variations of the system, or of the iterative procedure will give 
randomly that another axis will be the largest, computer calls this axis z, and 
you obtain EFG of another sign. 
Look at eta. It is (vyy-vxx)/vzz, and if it is equal to 1 or close, it is this 
case.

Best regards,
Lyudmila Dobysheva
--
Physics-Techn.Institute,
Udmurt Federal Research Center, Ural Br. of Rus.Ac.Sci.
426000 Izhevsk Kirov str. 132
Russia
---
Tel. +7 (34I2)43-24-59 (office), +7 (9I2)OI9-795O (home)
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Re: [Wien] EFG: theory Vs experiment for a case

[Stefaan Cottenier]

Most EFG experiments measure the absolute value only, hence you usually do not 
know the experimental sign.

The meaning of the sign is the same as for any derivative: a negative Vzz means 
that d Ez/dz is negative: the value of the z-component of the electric field 
becomes *smaller* if you go along the positive z-axis.

Stefaan


From: Wien  On Behalf Of Ashwani Kumar
Sent: Friday, December 14, 2018 6:33 PM
To: wien 
Subject: [Wien] EFG: theory Vs experiment for a case

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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