[Pw_forum] How to achieve the convergence of Ecutrho?

[GAO Zhe]

Actually, the standard of convergency for cut-off energy is not how much dE the system gained, but whether dE/dCut is near to 0 enough. Definitely, such a threahold, for dE/dCut, is also determined by yourself.
The example from you was too extreme. Thinking about 100Ry as step, your result are too rough to hold the slope information. But when 10^(-5)Ry was using, even though it should give the very fine dE/dCut information as well, the results may be not good due to the accuracy of DFT, numerical methods, and computer limitation ( please consider the length of float and double float variable ).
P.S.: Therefore, I think such question is not the one of sci. & tech. rather than your thinking method. This may be the reason that no person reply such a post in emuch.


--
GAO Zhe
CMC Lab, Materials Science & Engineering Department,
Seoul National University, South Korea
 



At 2011-12-13 15:43:04,"陶鹏" <ptao10b at imr.ac.cn> wrote:
>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!
>
>Yours,
>Plato Tao
> 
>--
>-------------------------------------------------------------------
>PH.D. candidate Peng Tao 
>Magnetism and Magnetic Materials Division
>National Laboratory for Material Science
>Institute of Metal Research, Chinese Academy of Sciences
>Phone  +86-024-83978751
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