[Pw_forum] Symmetry in PWSCF 1.3.0 - were there any bugs?

[Konstantin Kudin]

 Hello,

 I found the origin of the issue. It appears that the
results I tried to match were obtained with a modified
code. I attached the relevant piece of explanation
below.

 Perhaps there could be an input parameter that would
let people use this ignored symmetry with a large
warning printed? Something like "use at your own risk"
... Or do such cases fail in 100% of situations?

 Kostya

Young-Gui Yoon writes:
**********************************************
For nonsymmorphic groups, the code do not search
thoroughly fractional translations. Therefore, I
modified the code to search fractional translations.
Then, Paolo let me know why he disabled the search. I
am quoting his reply.
I removed the modification again (I don't remember
where it was, but it is simple.)

YG


======================================================================
Hi

>  2. In PWSCF, nonsymmorphic space group search has a
bug.

I don't think so: there is a tricky problem with
fractionary 
translations.
What happens is that a symmetry operation with a
fractionary 
translation
is not accepted if identity has also a fractionary
translation (which 
means
that the cell is a supercell). When this happens,
fractionary 
translations
are disabled, because even if good sym.ops. with
fractionary 
translations
are generated, there is no guarantee that they form a
group.

I encountered this problem years ago and found no
solution other than
disabling fractionary translations altogether in that
case. There might 
be
a solution, but the one you propose may not work in
some  cases.

Paolo

-- 
Paolo Giannozzi             e-mail: 
giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050509412
Piazza dei Cavalieri 7      Fax:     +39/050509417,
050563513
I-56126 Pisa, Italy         Office:  Lab. NEST, Via
della Faggiola 19

======================================================================



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