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["Mike" <xw23@163.com>]

I conducted a response function calculation and then used IFC to analyze DDB 
file, but I got the ERROR as follows:

  The lowest mode appears to be a "true" negative mode,
  and not an acoustic mode. This precludes the computation
  of the frequency-dependent dielectric tensor.
  Action : likely there is no action to be taken, although you,
  could try to raise your convergence parameters (ecut and k-points).
 For your information, here are the four lowest frequencies :
 -1.44436452E-03 -1.44432637E-03 -1.40826927E-03 -1.00781976E-03

 leave_new : decision taken to exit ...

I have tried several kinds of pseudopotentials and large ecut but there was 
no luck. Could anyone give me reasons why that happens and how to cope with 
it?
Thanks. 

          　　　　xw23@163.com
　　　　　　　　　　2002-09-02