[Pw_forum] finite dielectric methods

[Stefano Baroni]

On Apr 29, 2007, at 11:31 PM, li niu wrote:

> Dear Paolo U,
>
> Thanks for your reply.I'm very interested for your finite electric  
> field method.
> The dielectric polarizability tensor can be calculated by taking  
> dinite differences of atomic forces.

NO: forces have nothing to do with the dielectric tensor. If you want  
to calculate the dielectric constant using finite electric fields  
(why? linear response is there exactly to avoid that), you will have  
to calculate finite differences of electric polarizations  
corresponding to different diractions of the applied field.

> I have several questions to ask you.
>

...

> 2. For the calculation of the  off-diagonal mixedterms, two  
> different electric fields are required. This need apply electric  
> fields of intensity  - 2h/1.414 ,
> -h/1.414, 0, h/1.414 and 2h/1.414 along the three different couples  
> of cartesian directions, and apply equations.
> But how can I apply simultaneously finite fields along two  
> different Cartesian directions in cp.x code?[ESSPRESSO-3.2]

here, I can hardly follow you. Two finite (or infinitesimal, for what  
matters) fileds applied along different directions make ONE electrc  
field directed along the the sum of the two. Aren't electric fields  
VECTORS?

SB

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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