[QE-users] QE automatically converge centered cell to primitive ?

[Husak Michal]

I understand that Qunatum Espresso on its will change centered cell to
primitive,not changing the overal symmetry ... It create equivalent descriptipn in lover system with primitive cell automatically  ...
And it change the crystallographic system and lattice parameters as well ....

The question is whatever it indicate this change somwhere and give the transformation matrix used for transforming the input to the output ...
So we can reconstruct from the QE output the standard crystallographic description based on standard space groups witch use centered cells (corresponding to coordinates and centered space group given at the input) ...
We can probably decipher what is QE doing internaly, but it will be more easy to have the used transformation in the output file ...

Michal
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Paolo Giannozzi <p.giannozzi at gmail.com>
Sent: Thursday, December 23, 2021 10:25:42 AM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] QE automatically converge centered cell to primitive ?

I am not sure I understand what you mean. If you supply the structure and atomic positions via the space group and Wyckoff positions, QE generates the primitive (smallest) unit cell and corresponding lattice. QE does not change the symmetry or the structure by its own will, unless there is a bug for your specific case. If you prefer the so-called "conventional" unit cell, you need to consider the atoms that are in the conventional unit cell but not in the primitive one.

Paolo

On Wed, Dec 22, 2021 at 5:07 PM Michal Husak <Michal.Husak at vscht.cz<mailto:Michal.Husak at vscht.cz>> wrote:
Hi

We had entered inside QE a structure described by fractional
coordinates (asymmetric unit cell)
and space group (C 2/c ) ....
 From the output we see QE had itself transformed the structure to
another space group and unit cell
(probably P 2/c  triclinic system) to get speed  of calculation ....

Question:
- does QE anywhere mention, this transformation was done ?
- does it anywhere give the used transformation matrix ?

We simply need to reconstruct from the QE the atom positions
corresponding to the original CIF data ....

Michal Husak
UCT Prague



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Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
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