[CPMD-list] question about CUTOFF

[Mark Kosmowski]

I've been choosing cutoff by making an unoptimized single energy vs. cutoff
energy plot (I'll usually use 25 Ry to 250 Ry in 25 Ry increments) and
deciding how "flat" I want the curve to be at my cutoff of choice.  This is
done knowing that the calculation as a whole will take longer to perform.
Since cutoff choice is based primarily on atomic species, I do not repeat
this analysis for a new species unless the new species contains elements not
previously examined in this fashion.

>From my limited experiences, if I am concerned about a 5 Ry cutoff
difference, I am probably not on the "flat" enough part of the curve.

For the Goedecker pseudopotentials available from the CPMD website I have
been using a cutoff of 150 Ry as an acceptable compromise.  The systems I am
looking at are small molecule solids.

Good luck!
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