[Pw_forum] 12 Beryllium atoms in the unit cell

[Stefano de Gironcoli]

it'a (0001) surface calculation with 12 layer + vacuum
stefano de Gironcoli

On 05/12/2011 05:24 PM, Amin Torabi wrote:
> Dear all,
>
> I have some problems in understanding the input file on page 27 of the
> following tutorial:
> http://www.ichec.ie/education_training/qe_workshop/material/02/tutorial_io.pdf
>
> My questions are:
>
> 1. According to Ashcroft&  Mermin (p.77), Beryllium is a Hexagonal Closed
> Packed crystal with c/a=1.56(A). Now, why do we have celldm(3)=16.0 in this
> tutorial?
>
> 2. Why do we have 12 atoms in the unit cell? Can anyone give me a reference
> or a plain explanation on this unit cell?
>
>
> Thanks in advance!
>
>
>
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