[Pw_forum] 12 Beryllium atoms in the unit cell

Amin Torabi amin.torabi at gmail.com
Thu May 12 17:24:43 CEST 2011

Dear all,

I have some problems in understanding the input file on page 27 of the
following tutorial:

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

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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