Re: [QE-users] any tool to get real space force constant from shifted q grid or manually q grid phonon calculations?

[Yi Wang]

Many thanks.

I will refresh the textbooks.

Best,

Yi Wang

On 5/10/2018 19:44，Lorenzo Paulatto<paul...@gmail.com> wrote：

Yes, I understand the cost of phonon is the critical part.

For clarification, I meant if I perform phonon calculation on less q points (not on full gamma centered MP grids),

This is not how force constants work: as they are the (discrete) Fourier transform of the dynamical matrix, they can only be computed accurately for points which are reciprocal to the q-points in the grid. 

Using shifted grids is a good trick when computing "square modulus" integrals, where the phase does not count. But the calculation of force constants is all about the phase, and shifted grids do not work very well for this case. 

The fact that you eventually want the DOS is a red herring, it is completely irrelevant to the problem.

Kind regards 

how could I get reliable real space force constants toward the calculation of DOS.

Yi Wang

Nanjing University of Sci. & Tech.

On 5/10/2018 12:42，Lorenzo Paulatto<paul...@gmail.com> wrote：

Hello, 

the cost of computing the phonon dos with matdyn is zero, compared to the cost of the phonon calculation itself. 

--
Lorenzo Paulatto
Written on a virtual keyboard with real fingers

On 10 May 2018 06:31, "Yi Wang" <wangw...@gmail.com> wrote:

Dear everyone,

As I understand, the q2r.x works only on gamma centered q grids for the DFPT calculations. However, is there any tool to calculate the real space force constant for the shift q points calculations and the manually q grid calculations?

If it is possible, I want to test the phonon DOS calculation on some smaller q grids for the sake of saving cost.

Thank for your guidance.

Yi Wang

Nanjing University of Sci. & Tech.

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