[Pw_forum] symmetries in pw.x

[Paolo Giannozzi]

On Tuesday 10 January 2006 16:36, Andrea Ferretti wrote:

> 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...).

it is not that simple: there are cases in which you may want a grid in 
the IBZ, such as for instance to calculate the DOS, or phonons at a finite
q-vector. Presently the number of input k-points is left unchanged if there 
is no evidence of further processing, such as tetrahedron, gaussian
broadening, q-vector for phonons etc, in the input data for the nonscf run

> therefore I guess that nosym = .TRUE. should be effectiveless

'effective' or 'effectless'? nosym=.true. does not do what its name would
suggest, i.e. increase the number of k-points because symmetry is not 
used; it actually prevents the increase of the number of k-points with 
reduced symmetry. It does, or should do, what is explicitly stated in the
INPUT_PW file. 

I am quite dissatisfied with the present implementation of the 
k-point+symmetry stuff: it is a stratification of different approaches, 
and it shows. If you want to try to disentangle this mess, PW/setup.f90 
is the place to start from

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
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