[Wien] electric field gradient EFG

[Stefaan Cottenier]

> "Finally, I found relaxation occurs
> in SrTiO3 due to oxygen vacancies. I want to calculate the EFG value
> of the Ti-O bond. I found that The (Vaa Vbb Vcc EFG Eta)values for 
> Nb are -2.18 -2.18 4.37 4.37 0.0 
> O are  -1.50 -1.50 3.03 3.03 0.0"
> 
> My question;
> Is the EFG is additive quantity? For example 
> i.e., EFG equals   7.40?

(I assume you mean Ti instead of Nb.) Not at all! First of all, you 
cannot calculate the EFG "of the Ti-O bond". You can calculate the EFG 
at the Ti-nucleus and at the O-nucleus (and in principle at any other 
point in the crystal, also if there is no nucleus there), but "EFG of 
a bond" does not have a meaning. The EFG at a given point (nucleus) is 
*influenced* by the bonds that atom makes with its neighbours, but it 
is still an EFG at a point, not an EFG of a bond. Adding Vcc 
components is completely meaningless.

Additionally: you specify 5 numbers above, but they are a bit 
redundant. What is called ":EFGxxx" in wien2k is by definition either 
Vxx, Vyy, or Vzz, more specifically, the one of this triplet with the 
largest absolute magnitude. Furthermore, eta depends on Vxx, Vyy and 
Vzz, and is therefore not new information. Finally, Vxx+Vyy+Vzz is 
always zero, and therefore you need to give only 2 of these three in 
order to know the third one. Conclusion: in your list of 5 entries 
there are only 2 relevant quantities. Usually EFG and eta are taken 
for this. The 3 other quantities needed to specifiy the 5 degrees of 
freedom of this spherical tensor of rank 2 are e.g. the three Euler 
angles that specify the Principal Axis System of the EFG with respect 
to the global axis system. This direction information is given as well 
in the EFG-block in case.scf, but not under the form of Euler angles.

Stefaan


> 
> With my grateful thanks 
> Alaa S Hamid
> 
> -----الرسالة الأصلية-----
> Ù
Ù†: wien-admin at zeus.theochem.tuwien.ac.at
> [mailto:wien-admin at zeus.theochem.tuwien.ac.at] بالنيابة عن
> Stefaan Cottenier
> تاريخ الإرسال: Wednesday, January 12, 2005 6:58 AM
> إلى: wien at zeus.theochem.tuwien.ac.at
> الÙ
وضوع: [Wien] Re: [Wien] ÑÏ: [Wien] electric field
> gradient EFG
> 
> 
> > One other question concerning the force and the relaxation;
> > What is the method (theory) that correlate the EFG to the atomic
> relaxation?
> 
> I'm not sure whether I understand what you mean. The EFG is
> determined by
> the anisotropy of the charge distribution near the nucleus. This
> charge
> distribution is affected by how the bonds with neighbouring atoms are
> made,
> and therefore with the position of these neighbouring atoms. If you
> move
> (relax) the neighbouring atoms, the EFG will change.
> 
> Does this answer your question ?
> 
> Stefaan
> 
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-- 
Stefaan Cottenier
Instituut voor Kern- en Stralingsfysica
K.U.Leuven
Celestijnenlaan 200 D
B-3001 Leuven (Belgium)

tel: + 32 16 32 71 45
fax: + 32 16 32 79 85
e-mail: stefaan.cottenier at fys.kuleuven.ac.be