[Pw_forum] How to achieve the convergence of Ecutrho?

[WF]

>Dear all,
>
>I've asked sevral people about the convergence criteria of Ecutrho test.
They point out that the convergence will be achieved when the difference
between two adjacent scf calculation is smaller than 0.1 meV. However, they
are not very sure about the step length. From my view, the step length may
pose huge effects on our calculation. Consider the cases of step lengths are
100 Ry and 0.00001Ry respectively, the latter will be convergent immediately
while the former will not be so fast.

>For the resons above, I'm really confused now. And could any nice guy show
me the strict judgement of the convergence for Ecutrho? Thank you very much!

The convergence of Ecutrho comes from the balance of time and accuracy, so
the judgment is based on your own system and there is no universal one.
Typically, 1Ry~10Ry should be step length under most circumstance, as one
can reach the convergence reasonably fast while the additional time cost
from the more than enough Ecutrho will be in the same order of magnitude as
10%, an acceptable value. 


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Wu Feng,
Chemistry and Molecular Engineering, Peking University
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