[Pw_forum] problem of cutoff convergence

[平远]

I forgot to attach the bandgap vs cutoff plot. We can see the big jump
clearly from this graph.
                                                       yuan ping
                                                    university of
california, Davis

2008/10/31 平远 <plain110 at gmail.com>

>  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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