The ABINIT Users Mailing List ( CLOSED )

[Patrick Welche <prlw1@newn.cam.ac.uk>]

I suspect this is a FAQ, but I didn't see any references to the
problem I see.. 

Essentially, I try an ionmov 3 optcell 2 calculation for a Cccm (spgroup 66)
crystal. My original input file just has the natrd 12 attoms in it, with
a (1,0,0)(0,1,0)(0,0,1) rprim, setting brvltt -1 to find the real rprim.
I just enter xred for the 12 atoms and let the spgroup find all natom 58.
(116 in the conventional orthorhombic unit cell)

Time passes and 30 Broyden steps later, I have not converged. So the
problem now is, how to restart where I stopped? (Maybe increasing ecut
from 25 to 35 at the same time) 

I cut and pasted the acell, rprim, xred, typat from the output file
back into the input file. As rprim now looks like a real primitive
unit cell, I thought I would take brvltt -1 out (and of course removed
natrd 12 as there are 58 atoms listed) 

This gave me the error:

 chkprimit : ERROR - 
  According to the symmetry finder, the unit cell is 
  NOT primitive. The multiplicity is  2 .
  The use of non-primitive unit cells is allowed
  only when the input variable chkprim is 0.
  Action : either change your unit cell (rprim or angdeg),
  or set chkprim to 0.

yet the rprim is essentially
(sqrt(3)/2,1/2,0),(-sqrt(3)/2,1/2,0)(0,0,1)
which seems right. For the conventional cell, I would expect multiplicity 2
as it is C-centered, with 116 atoms. 

For no logical reason, I put brvltt -1 back in, and get:

 chkorthsy: ERROR -
  The symmetry operation number    3 does not preserve
  vector lengths and angles.
  The value of the residual is  6.1161E+04.
  Action : modify rprim, acell and/or symrel so that
   vector lengths and angles are preserved.
   Beware, the tolerance on symmetry operations is very small.
        
So I am confused: the calculation used the symmetry and gave me an output
file. How come I need to modify the output? (Should I not have picked xred
but rather xcart or some other version of the coordinates?)
        
Cheers,
        
Patrick 

P.S.: I use getwfk -1 during the calculation, but then it seems I can't
make use of the last _WFK file, as apparently at most one of getwfk and
irdwfk can be non zero. Is there a way of not starting again from a random
wavefunction?