[Pw_forum] Interatomic force constant

[Stefano Baroni]

Dear Mr. Onaiwu,

Quantum ESPRESSO can calculate IFCs from first principles, and then it has small utilities for calculating phonon dispersions from the calculated IFCs. Of course, it does not make any sense to sense to "change" the IFCs calculated from first principles, because the ICFs are the *output*, not the input, of the calculations. Once the IFCs are calculated and stored, as said, they can be used to calculated vibrational dispersions. Nothing forbids to change the calculated IFCs for further reuse, provided one knows what one is doing, and why.

This being said, it seems to me that the pw forum would be the ideal arena for discussions such as the present one. For that reason, I am forwarding my reply to your enquiry to the forum as well.

Best regards,

Stefano Baroni

On Sep 8, 2011, at 11:33 PM, Onaiwu Kingsley Nosa wrote:

> Dear Stefano,
> I'm presently doing a phonon calculation of graphene in my Ph.D
> research. Please, I'd want to know if there is any way that the
> interatomic force constant can be changed in the Quantum espresso
> code. I'd be grateful of any assistance in this regard.
> Kingsley Onaiwu

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

La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget

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