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<div class="moz-cite-prefix">Dear David,<br>
I think that the relative (crystal) coordinates that you write for
the 5-atom cell are still expressed in terms of the conventional
cell (the one with vectors (a,0,0), (0,a,0), (0,0,c). This is the
cell used in the case ibrav=14, reason for which you get the
correct structure.<br>
<br>
Instead, the cell used in ibrav=7 is the primitive one - the docs
say:<br>
<br>
v1=(a/2)(1,-1,c/a), v2=(a/2)(1,1,c/a), v3=(a/2)(-1,-1,c/a)<br>
<br>
Therefore you have to express the relative (crystal) coordinates
with respect to this basis set, and not in terms of the lattice
vectors of the conventional cell.<br>
<br>
Best,<br>
<br>
Giovanni Pizzi<br>
<br>
<br>
<br>
On 05/27/2014 03:48 PM, David Foster wrote:<br>
</div>
<blockquote
cite="mid:1401198482.30879.YahooMailBasic@web125406.mail.ne1.yahoo.com"
type="cite">
<pre wrap="">Dear users
The atomic positions for BaNi2As2 crystal with space group of I4/mmm (139) are:
Ba (2a): 0, 0, 0
As (4e): 0, 0, 0.3471
Ni(4d): 0, 0.5, 0.25
I used MS Visualizer to build the conventional tetragonal cell (a = b = 4.1474 c = 11.619).
After seeing the structure with MS, I convert it to primitive and finding all atoms positions. Only 5 atoms there are in primitive (If I am right):
Ba 0.000000 0.000000 0.000000
As 0.347100 0.347100 0.000000
As 0.652900 0.652900 0.000000
Ni 0.750000 0.250000 0.500000
Ni 0.250000 0.750000 0.500000
I prepared two input file for QE5.0.3, one with ibrav=7 and 5 atoms, and the other with ibrav=14 and all atoms in conventional cell instead of its primitive:
with P1 symmetry, the cell has 10 atoms:
Ba 0.0000 0.0000 0.0000
Ba 0.5000 0.5000 0.5000
As 0.000 0.000 0.3471
As 0.5000 0.5000 0.8471
As 0.000 0.000 0.6529
As 0.5000 0.5000 0.1529
Ni 0.000 0.5000 0.25000
Ni 0.500 0.0000 0.250000
Ni 0.000 0.5000 0.75000
Ni 0.500 0.0000 0.750000
I have attached two inputs and two pictures that xcrysden shows. While ibrav=14 shows the crystal correctly, ibrav=7 has a problem and doesn't show the crystal properly. I am confused!!
Any help will be appreciated.
Then, I
Regards
David Foster
Ph.D. Student of Chemistry</pre>
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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Giovanni Pizzi
Post-doctoral Research Scientist
EPFL STI IMX THEOS
MXC 340 (Bâtiment MXC)
Station 12
CH-1015 Lausanne (Switzerland)
Phone: +41 21 69 31124</pre>
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