I am running some tests on the wurtzite structure (CdS) and I find some strange results.
First, in my INPUT file, when I use RPRIM to define the cell, the space group determined by abinit is Cmc21 (No 36) instead of P63mc (No 186).
My INPUT file looks like:
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NATOM= 4
NTYPAT= 2
TYPAT= 1 1 2 2
ZNUCL= 48 16
XRED
0.66666667 0.33333333 0.50000000
0.33333333 0.66666667 0.00000000
0.66666667 0.33333333 0.87500000
0.33333333 0.66666667 0.37500000
ACELL
4.141 4.141 6.720 angstrom
RPRIM
0.500 -0.866 0.000
0.500 0.866 0.000
0.000 0.000 1.000
Is there a mistake in my definition of the crystalline structure?
Second, I've looked in the forum and I've seen that people usually use ANGDEG and SPGROUP to build a wurtzite structure. So I've replaced the RPRIM keyword in my INPUT file:
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ACELL
4.141 4.141 6.720 angstrom
ANGDEG 90. 90. 120.
SPGROUP 186
but in this case I end up with Abinit crashing with the following message:
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Subroutine Unknown:0:WARNING
Trouble finding symmetrically equivalent atoms
Applying inv of symm number 2 to atom number 2 of typat 1
gives tratom= 6.6667E-01 3.3333E-01 -5.0000E-01.
This is further away from every atom in crystal than the allowed tolerance.
The inverse symmetry matrix is 0 -1 0
1 1 0
0 0 1
and the nonsymmorphic transl. tnons = 0.0000000 0.0000000 0.5000000
The nearest coordinate differs by 1.110E-16 1.000E-08 0.000E+00
for indsym(nearest atom)= 1
forrtl: severe (27): too many records in I/O statement, unit -5, file Internal Formatted Write
What surprises me is:
The nearest coordinate differs by 1.110E-16 1.000E-08 0.000E+00
This is definitely a small difference. Abinit shouldn't stop right?
Thank you for your help.
Boris