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

[Paolo Giannozzi]

On Thu, Dec 23, 2021 at 3:51 PM Husak Michal <Michal.Husak at vscht.cz> wrote:

We can probably decipher what is QE doing internally
>

no need to do that. You have in output the primitive cell and atoms in the
primitive cell. You find what you call the "standard" cell, presumably the
corresponding  "P" one (the primitive cell is "F", "I", whatever), n times
larger (n=2 or 4) than the primitive cell. Then you look for n lattice
points in the primitive cell that are not lattice points of the "standard"
cell. Or at least, this is my understanding of your problem

Paolo

________________________________
> 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,
> Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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