[Pw_forum] scan the lattice constant-seems not a closed question

W. YU yuwen_66 at yahoo.com
Tue Sep 13 03:53:14 CEST 2005

Thanks to Nicola,

I really took the charge density cutoff as ecutoff in
the former question. Sorry!

But I still have two questions: First, in the diamond
case, the lowest energy at an ecutoff seems closer to
the left side of the red curve(ecutoff=26Ryd)(which is
on the small lattice parameter side) and this seems to
be contradictory to the more plane wave basis fact at
small lattice constants. (but there is no such a
problem for the ecutoff=24Ryd case, why)

Second, still comes from the diamond case. As can be
seen from the curves at fixed ecutoffs, the lowest
energy seems to rise with increasing ecutrho from 160
to 200 Ryd and drops from 200 to 240 Ryd. But the
energy at 240 Ryd is still higher than at 160 Ryd. I
also met this fact when checking the ecutrho at a
fixed ecut in my former calculations. Here the
question is: What is the relationship between ecutrho
and the total energy (if monotonic lowering of the
energy with increasing ecutrho is not always the case)

Best regards,


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