# [Pw_forum] Quick question on coordinates

Miguel Marti­nez miguel.martinez at ehu.es
Wed Feb 27 17:21:30 CET 2008

Dear Paolo,

First of all thanks for your helpful answer. In any case, if
flib/latgen.f90 says:

else if (ibrav == 12) then
sen=sqrt(1.d0-celldm(4)**2)
a1(1)=celldm(1)
a2(1)=celldm(1)*celldm(2)*celldm(4)
a2(2)=celldm(1)*celldm(2)*sen
a3(3)=celldm(1)*celldm(3)

Then the documentation seems to have sin(gamma) and cos(gamma) mixed for
ibrav=12. Nothing harmful, though.

Paolo Giannozzi escribió:
> The case ibrav=13 has been corrected more than once by the way.
> If you have evidence that there is something wrong above, please
> explain what exactly and why

Truth to be said, the only evidence I have is my lack of skill in putting
the coordinates of a C2/C crystal in ibrav=13, when the full positions work
OK in ibrav 12. I must be doing something very very silly.

By the way, I'm sure there is a reason why the special axis in quantum
espresso is c while the tables love to use axis b. Even if the answer is
like, "if crystallographers don't put 2\pi everywere, we don't like their
basis sets".

--
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Miguel Martínez Canales
Dto. Física de la Materia Condensada
UPV/EHU
Facultad de Ciencia y Tecnología
Apdo. 644
48080 Bilbao (Spain)
Fax:  +34 94 601 3500
Tlf:  +34 94 601 5326
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