[Pw_forum] symmetries in pw.x

[Andrea Ferretti]

Dear all,
I went through a problem with symmetries and I would like to better 
understand how they actually work in espresso (pw.x particularly):

as far as I understand, in scf calculation both time-reversal and 
space-group symmetries are used to define the irreducible wedge in the BZ 
in order to compute BZ sums (total energy, charge density etc...).

my question is about non-self consistent calculations:
what I expected is that no symmetrization should be performed (e.g. when 
I compute band structure for silicon along a specific symmetry line it 
makes no sense to me to define weights and so on...).

therefore I guess that nosym = .TRUE. should be effectiveless in nscf 
calculations, while I have been reported about the contrary...
the problem seems to be connected with weights, which, even if not used 
(I guess) in nscf are anyway internally calculated and reported in the 
output file... is it an expected behavior ??
(sorry, at the moment I have no input file at hand demonstrating 
 the fact, but if needed I will provide it as soon as possible...)

my question is at this point about the actual implementation of 
symmetrization (and nosym) both in scf and nscf calculations...
can anyone comment on this point ??

by the way: setting nosym = .TRUE. together with automatic generated kpt 
meshes make some symmetry reduction in kptnumber anyway: I guess it is due 
to the time-reversal symmetrization which is still around... is it true ??


sorry for the long email, and thanks for any support...
cheers 
Andrea


-- 
Andrea Ferretti
INFM National Research Center on nanoStructures and bioSystems at Surfaces (S3)
Dipartimento di Fisica, Universita' di Modena e Reggio Emilia
Via Campi 213/A I-41100 Modena, Italy
Tel:     +39 059 2055283
Fax:     +39 059 374794
E-mail:  ferretti.andrea at unimore.it
URL:     http://www.nanoscience.unimo.it

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