[Pw_forum] esp_0 for LaAlO3

[Stefano Baroni]

Dear Hanghui: I am not very familiar with (nor very fond of) finite- 
electric-filed calculations.
I agree that a finite electric field should produce a finite force on  
the atoms of a polar material, such al LaAlO3. Why it does not, in  
your case, I do not know. You may want to provide more info on the  
details of your calculation.
As for your general question, the answer is contained in any textbook  
of lattice dynamics. One readable reference (as opposed to the rather  
unreadable, though classic Born and Huang, dynamical theory of crystal  
lattices) is Harald Bottger, Principles of the theory of lattice  
dynamics. The necessary algebra in a simplified form (although not the  
final result) can be also found in our RMP paper:

@article{Baroni-RMP:01,
	Author = {Baroni, Stefano and de Gironcoli, Stefano and Dal Corso,  
Andrea and Giannozzi, Paolo},
	Journal = {Rev. Mod. Phys.},
	Number = {2},
	Pages = {515-562},
	Title = {Phonons and related crystal properties from density- 
functional perturbation theory},
	Volume = {73},
	Year = {2001}}
see eqs. 89 & ff.

Cheers - SB

On Jul 23, 2008, at 5:22 PM, alan chen wrote:

> Dear Stefano,
>       Thank you very much for your previous email.
>       However, I am now calculating esp_0 of bulk LaAlO3. For a  
> polar material with large dielectric constant, I expect esp_0 is  
> much larger than esp_infty. But since all the forces on the atoms  
> are zero,  the code does not know how to move the atoms when I relax  
> them.
>       By the way, how to calculate esp_0 in principle? Shall I relax  
> the structure while turning on the electric field?
>        Sorry to bother you again.
>
> Hanghui
> Department of Physics,
> Yale University

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

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