Hi, i tested a relaxed sapphire structure using a 10x10x10 k point set with a cutoff energy up to 250 Ry. Even at this Energy, a change of +/- 5 Ry in the cutoff lead to stresses of the order of 1 kbar. I used for Al and O pbe-n-van US pseudo potentials from the pseudo folder of quantum espresso. But also pbe-sp-van for Al and rrkjus for oxygen led to the same problem. I don't have a clue how high the cutoff must be, but 250 Ry seems to be far too high. Is that a problem of the pseudopotentials or does it have something to do with physical structure of sapphire? Thx for any hints, J?rg Buchwald
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