[Pw_forum] 2nd and 3rd energy derivatives using DFPT?

[stefano de gironcoli]

the third derivatives that are computed in D3 are those of type 
d3E/du(q) du(-q) du(0) where at least one q-vector is 0.
For the generalization to any set of displacements you need to wait for 
Lorenzo's contribution.

stefano

On 20/04/2016 14:51, Sabry Gad Al Hak Moustafa wrote:
> Thanks Stefano;
>
> But, what do you mean by "some"? I am interested specifically in Fe at 
> high pressure, so, can QE do 3rd derivative for that?
>
> Here
>
> http://www.quantum-espresso.org/wp-content/uploads/Doc/ph_user_guide.pdf
>
> it says
>
> "D3/d3.x: calculates anharmonic phonon lifetimes (third-order 
> derivatives of the energy), using data produced by pw.x and ph.x (USPP 
> and PAW not supported)."
>
> So, it looks like it is NCPP.
>
> Thanks;
> Sabry
>
>
>
> ==================================================
> Sabry G. Moustafa, Ph.D.
> Department of Chemical and Biological Engineering
> 511 Furnas Hall
> University at Buffalo, The State University of New York
> Buffalo, NY 14260-4200
> 716-645-1186 (office)
> 716-239-8543 (cell)
> E-mail: sabrygad at buffalo.edu <mailto:kofke at buffalo.edu>
>
> On Wed, Apr 20, 2016 at 12:28 AM, stefano de gironcoli 
> <degironc at sissa.it <mailto:degironc at sissa.it>> wrote:
>
>     the phonon code evaluates second order derivatives (dynamical
>     matrices).
>     this is available for NCPP, USPP and PAW
>
>     the D3 code computes some of the third order derivatives.
>     it is working for NCPP only as far as I remember.
>
>     forth order derivatives are not computed.
>
>     stefano
>
>
>     On 20/04/2016 06:34, Sabry Gad Al Hak Moustafa wrote:
>>     Hi;
>>
>>     Was wondering if QE can compute 2nd, 3rd and 4th energy
>>     derivatives in the DFPT framework? If so, is available in PAW, or
>>     just PPs?
>>
>>     Thanks;
>>     Sabry
>>
>>
>>
>>     ==================================================
>>     Sabry G. Moustafa, Ph.D.
>>     Department of Chemical and Biological Engineering
>>     511 Furnas Hall
>>     University at Buffalo, The State University of New York
>>     Buffalo, NY 14260-4200
>>     716-645-1186 (office)
>>     716-239-8543 (cell)
>>     E-mail: sabrygad at buffalo.edu <mailto:sabrygad at buffalo.edu>
>>
>>
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