[QE-users] crystal definition

[Stefano Baroni]

Valeria: your question is answered, e.g.,  at page 10 of the eighth edition of Kittel’s solid state textbook. I am afraid you’ll have to go through as many as 9 pages to arrive at the point, but they are full of figures. Hope this helps. SB

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Stefano Baroni, Trieste -- http://stefano.baroni.me

> On 31 Jan 2021, at 07:39, Husak Michal <Michal.Husak at vscht.cz> wrote:
> 
> Forget this method.
> Get a CIF file for the structure you want to stady and
> use the space group based crystal definition ...
> ________________________________
> From: users <users-bounces at lists.quantum-espresso.org> on behalf of valeria arteaga muñiz <valitzelar at hotmail.com>
> Sent: Sunday, January 31, 2021 5:26:37 AM
> To: users at lists.quantum-espresso.org
> Subject: [QE-users] crystal definition
> 
> Hello everyone.
> 
> I have been working for a couple of months with quantum espresso and still there are some things that get me confused. I hope you can help me.
> If we wanted to define a BCC crystal (lets say) we could make use of the ibrav=3 parameter. With this, we would have a bcc structure with one atom per cell (?). I don’t know how can that be possible if the bcc cell is supposed to have two atoms per cell (1/8 contribution of  8 corner atoms + 1 contribution of a middle atom). When I use xcrysden for visualization just setting ibrav =3, I get the complete bcc structure.
> 
> I also have tried to create my bcc crystal from scratch using ibrav=0 and placing the atomic positions at the corner and other atom at 0.5 0.5 0.5 (center), which leads to 2 atoms per unit cell. When I make scf calculations for this case I get around twice the total energy I get in previous case (using ibrav=3). I wonder what is the correct way to use this.
> 
> 
> Thanks for your clarifications,
> Valeria
> 
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