[Pw_forum] atomic displacements in phonon calculations

[Azadi, Sam]

Dear Lorenzo, 

Thanks for your reply. 
I may missing something here, I appreciate if you explain. 
How do you define the amplitude of u(R) vector in derivative calculations? 
3N normal coordinates related to 3*N normal modes are displaced compared to relaxed positions, if I’m right.

Best, Sam

 
> On 1 Mar 2017, at 11:36, Lorenzo Paulatto <lorenzo.paulatto at impmc.upmc.fr> wrote:
> 
> On Wednesday, March 1, 2017 11:54:01 AM CET Azadi, Sam wrote:
>> Dear Experts,
>> 
>> I’m interested to know that how the amplitude of atomic displacements are
>> defined in DFPT calculations? 
> 
> Hello, in density function perturbation theory, contrary to finite-differenes 
> method, there is no atom displacement: quantum-mechanics perturbation theory 
> is used.
> 
> See this reference: <http://journals.aps.org/rmp/abstract/10.1103/RevModPhys.
> 73.515> for details on the method how it is implemented in QE.
> 
> Tis lecture from Stefano Baroni to get a quick idea: < https://
> www.dropbox.com/s/xi06fv6oz07j9du/EUSPec%202016%20%281%29.pdf?dl=0>
> 
> 
> -- 
> Dr. Lorenzo Paulatto 
> IdR @ IMPMC -- CNRS & Université Paris 6
> phone: +33 (0)1 442 79822 / skype: paulatz
> www:   http://www-int.impmc.upmc.fr/~paulatto/
> mail:  23-24/423 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
> 
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