[Wien] Bandgap of ionic bonds

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 Hello Wien2k users,

  I have begun to study a bandstructure of a relatively new semicondutor supposed 
  to have a strong ionic bonding. 

  The bandgap calculated is about the 1/10 of the experimental one(1 eV).  I tryed three 
  exchange-correlation energy functions recommended in the WIEN2K 
  but the result is same. I once heard that other types are also available as hidden options.

  Does anyone show me, if it is so, how to use other functions and which one is 
  probaly appropriate for more ionic materials ? Is there are any physical reason for 
  a suitable exchange-correlation for ionic materials rather than covalent bonds ?

  One more complicataion; if I increase the R*Kmax value to 8 or higher, the bandgap disappears.
  The total energiy decreases, of course.  Any suggestions are very much appreciated for this 
  behavior.

  Thank you very much.

  K.Takarabe/Okayama University of Science, Japan