[QE-users] Format of FFT grid for Potential

[Shivesh Sivakumar]

Dear Paulo,

That clarifies my doubt. Thank you very much.

Best,
Shivesh

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From: users <users-bounces at lists.quantum-espresso.org> on behalf of Paolo Giannozzi <p.giannozzi at gmail.com>
Sent: Saturday, October 10, 2020 2:04:21 PM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Format of FFT grid for Potential

On Sat, Oct 10, 2020 at 5:52 AM Shivesh Sivakumar <shiveshsivakumar at gmail.com<mailto:shiveshsivakumar at gmail.com>> wrote:

For instance, my FFT grid has dimensions 40x54x180. If I understand correctly, this means:
1) The lattice constant along 'a' is divided into 40 points, along 'b' is divided into 54 points and so on..

in general, what is divided into 40, 54, 180 points are the three primitive lattice vectors generating the lattice

2) There are a total of 388800 (40*54*180) points printed, which correspond to the potential at each point , starting with varying 'x' first, then 'y' and then 'z'. Meaning,
the first 40 points in the output should be (0,0,0), (0.025,0,0) ... (1,0,0).

(1,0,0) would be point 41 but is not in the grid, because it is equal to (0,0,0) (if your plot seems to miss something, that's why). Same for the two other directions. Xcrysden should output data in the same order as in FFT arrays: see point 6.3 of the developers' manual,  https://www.quantum-espresso.org/Doc/developer_man/developer_man.html

Paolo

The next 40 points should be                   (0,1,0), (0.025,1,0) .. (1,1,0).

Am I right in this regard? Any help would be much appreciated.

Thanks,
Shivesh Sivakumar
University of Washington-Seattle
WA-98105
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