[Pw_forum] Total Energy doesn't converge upon increase in Ecutwfc

[Han Chueh]

Dear all,

It is my understanding that as one increases the cutoff energy for the
wavefunctions, Ecutwfc, the total energy of a given structure should
converge towards a minimum. However, when I did this in the case with GaN
with GGA, it did not seem to converge and kept dropping energy more as I
increased the Ecutwfc. Why is this happening? I will include a sample input
file and Excel file showing this behavior.

>From the Excel graph, one can see that the total energy appears to converge
between 50 Ry and 70 Ry but then began to drop rapidly after that. It
appeared to converge again between 100 and 200 Ry but again dropped down
rapidly after that.

Sincerely,

Han Chueh
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