[Pw_forum] 12 Beryllium atoms in the unit cell

[Amin Torabi]

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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