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[Walter Lambrecht <walter.lambrecht@case.edu>]

Hi Xavier,
Thanks. That is what I was afraid of. We're doing some calculations on 
ZnGeN2 and related materials. I am not sure if it is important at this 
point since there are no measurements or good crystals of this material 
yet. It would just have been a bit more complete by adding this.
I am not sure I am ready for giving it a try within abinit. I have no 
experience with its source code, really, nor the man power, i.e.
competent programmer student to do it.  Sorry.
Walter



Xavier Gonze wrote:
> Dear Walter,
>
> On 22 Jul 2008, at 21:18, Walter Lambrecht wrote:
>
> > In Veithen et al. PRB 71, 125107 (2005) it is described how to  
> > calculate the
> > linear electro-optic
> > tensor in the unclamped condition, i.e. including the piezoelectric
> > contribution under zero external
> > stress. From eq. A15, it appears that what is needed is the Raman  
> > tensor, the
> > force in response
> > to strain internal strain tensor for the second term and the  
> > derivatives of the
> > high frequency dielectric  tensor  vs. strain components in the  first 
> > term.
> > At present it appears like I would be able to extract all the  necessary
> > pieces from the anaddb results for the second term but not the  first 
> > term. Are
> > the
> > third derivatives of the type: two vs. electric field and one vs.  
> > strain being
> > calculated by abinit
> > and where can I find them in the DDB files?
>
>
> Unfortunately, this third-order derivative of the energy has not been  
> coded (yet ...).
> Marek performed that computation by finite difference of dielectric  
> tensor for different
> primitive cells.
>
> > or what variable needs to be set in
> > the input
> > to generate these? Or better, has this procedure been implemented  in 
> > anadbb?
> > Alternatively is the anadbb capable of generating the elasto-optic  
> > tensor
> > directly?
> > Sincerely,
> > Walter Lambrecht
>
>
> Best regards,
> Xavier

--
Walter R. L. Lambrecht,
Department of Physics, Case Western Reserve University
Cleveland, OH-44106-7079 (216)368-6120 fax (216) 368-4671
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