[Pw_forum] [Fwd: diagonalization failure (david, cg) for large numbers of bands]

[Brad Malone]

Joseph,

I've never tried computing quite that many bands (only gone up to about 1200
bands) or with that many atoms per cell. However, I've never not been able
to get the bands to converge using both 'cg' diagonalization and also with
increasing the cutoff. You mentioned that you have tried increasing the
cutoff, but perhaps you haven't gone high enough?

Here is a quote from Paolo that might be relevant in your situation:


the algorithm used in PWscf is based on the assumption that
> the number of Kohn-Sham states (aka bands) is much smaller
> than the number of basis functions (i.e. plane waves). If this
> assumption doesn't hold (and it doesn't if you calculate 500
> bands in fcc Si unless you use a very large cutoff) you may
> run into trouble. Moreover iterative diagonalization becomes
> slower and more memory-consuming than conventional
> diagonalization. If you really need to do that, you need to
> modify the code
>
>
Best,
Brad Malone
UC Berkeley
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