[Pw_forum] problem of cutoff convergence

[平远]

 Hi,
  I met a problem with cutoff convergence when I ran the Si nanowire self
consistent calculation to get the lda band gap.
  I found a big jump 0.3-0.4ev of band gap at 45Ry. Before and after this
point, the band gap curve is flat.
   (HOMO does not change much, but lumo had a big jump. )
  And the position of this jump will shift with different structure (before
I relaxed the structure, this big jump was at 30Ry.)
 I used Si.pz-vbc.UPF, H.pz-vbc.UPF, poseudopotential to run this
calculation.
  I found similar thing when I calculate silane band gap. The jump of 0.4ev
happens at 60-65Ry. And I used the same poseudopotential to calculate.
   So what can be the  reason for this big jump in band gap with respect to
cutoff?
               thank you very much!

yuan ping

university of california, Davis
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