[Pw_forum] D3.x limited to Gamma point?

[Stefano Baroni]

On Nov 30, 2012, at 6:35 PM, Badescu, Stefan wrote:

> Greetings,
>  
> I am trying to understand a detail of the D3 suite. Some literature suggests that it can be used to calculate the decay of phonons at any q-point.

The theory being the code can. The code itself, I am afraid, cannot ...

> Looking at the code and at the inpt required by d3.x though, my first interpretation is that it works for Gamma phonon decaying through a q,-q channel.

right

>  In the calculation of force constant derivatives, the d3.x program requires
> the perturbed densities at q0=0 and at the q of the decay channel, producing V^(3)(0,q,-q) .
> To calculate V^(3)(k,q,k-q), does it make any sense to input fildrho given by a calculation at q, and  fild0rho given by a calculation at k?

I am afraid it does not ...

> The calculation seems to work but I am not sure whether it is meaningful, i.e., whether this can be used to calculate the decay of a k-point phonon through q and a k-q phonons.

I think that the way from "producing numbers" to "actually working" (i.e. producing meaningful numbers) is a long one. The habit to use ready-to-use complex computer codes may sometimes make it seem shorter ...

As far as I understand, the "long way" is actually being walked by Francesco Mauri's group in Paris.

Stefano


---
Stefano Baroni -  http://stefano.baroni.me, stefanobaroni (skype)
on leave of absence from SISSA, Trieste, presently at the Department of Materials, EPF Lausanne (untill March 2013)

I believe in the despotism of human life and happiness against the liberty of money and possessions - John Steinbeck

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