[Pw_forum] too many bands are not converged

[Chad Junkermeier]

Hello Pw_forum,
   I was working on a model system using a 2x2 supercell, everything  
worked fine.  I switched a 4x4 system and I repeatedly get the  
following error:
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
%%%%%%%%%
      from c_bands : error #         1
      too many bands are not converged
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
%%%%%%%%%

The only changes I made to the input file were nat, ATOMIC_POSITIONS,  
and K_POINTS.  The changes to nat and ATOMIC_POSITIONS, are obvious  
due to the increase in cell size.  In moving to the larger supercell I  
went from

K_POINTS automatic
4 4 1  0 0  0

to

K_POINTS automatic
2 2 1  0 0  0

What is the general cause of the error?  Is there a change to the  
input that normally solves this problem?

Chad Junkermeier, Ph.D.
NRC Post-Doctoral Fellow
Naval Research Laboratory
4555 Overlook Ave, S.W.
Washington DC 20375