[Wien] Ghost band come from large charge fluctuation

Wed Mar 2 12:14:02 CET 2005

I'm not very familiar yet with the new mixing techniques, but mixing parameter of 10^-6 strikes me as completely ridiculous.
If you do not allow the density to move at all, it will surely not make crazy jumps - is that the philosophy?

Kevin Jorissen

EMAT - Electron Microscopy for Materials Science   (http://webhost.ua.ac.be/emat/)
Dept. of Physics

UA - Universiteit Antwerpen
Groenenborgerlaan 171
B-2020 Antwerpen
Belgium

tel  +32 3 2653249
fax + 32 3 2653257
e-mail kevin.jorissen at ua.ac.be

________________________________

Van: wien-admin at zeus.theochem.tuwien.ac.at namens liyh
Verzonden: wo 2-3-2005 2:58
Aan: wien at zeus.theochem.tuwien.ac.at
Onderwerp: Re: [Wien] Ghost band come from large charge fluctuation

Dear. L. D. Marks,

     I didn't find the :PLANE and :DIRB value in the case.scf file.
Did these value add in wien2k_05.1?
My input structure file is in the attachment, could you give me some suggest
about mixing? As Peter said, I use PRATT and original case.in1 file,and set the mixing
parameter to 0.000001, I found the program can run, but I am not sure if I can get a
converged result. For gaasv9_Ga (36 atoms) we can get a converged result using 0.01 mixing
parameter and PRATT, but for gaasv12Ga_VFF (48 atoms) the mixing parameter must set top 0.000001!
Could you please check it for me?

Best Wish to You!

Yonghua

Fudan Univ, China

>In addition to the points Peter made about using the original case.in1 and
>not using -in1new until you are close to the solution (and not being too
>concerned about ghostbands until you are close), let me add something
>about mixing.
>
>Please, DO NOT SIMPLY REDUCE THE MIXING FACTOR. A rather major change in
>the mixing was made a couple of releases ago:
>       1) Introduction of a plane wave scaling term (PW)
>       2) Addition of an output of the plane wave convergence :PLANE
>       3) Addition of a diagnostic parameter :DIRB
>       4) Addition of an auto-restart of the Broyden cycle
>
>In iterative numerical methods scaling is VERY important, and has a
>huge effect. The UG is not very detailed about these (Peter: perhaps
>should add something, perhaps even a FAQ). I've attached a file "Check"
>which I suggest you put in your $HOME/bin and run every now and then to
>monitor the progress.
>
>Key points:
>       a) :DIRB gives the modulus of the Broyden step the algorithm is
>using, the modulus of the Pratt step (it does not use it) and the angle
>between the two. If this angle is more than about 45 degrees in 99% of the
>cases this means that your plane scaling term is too large. Reduce it,
>remove *bro* files and continue. (I prefer a value of 0.25 for my initial
>estimate of this, smaller than Peter's default of 0.5, not sure which is
>"best".) If the angle gets really large, > 138 at present, the algorithm
>abandons the previous Broyden history and restarts with a small Pratt
>step.
>       b) In most cases "sloshing" is due to poor convergence of the
>plane waves (:PLANE). If the atomic-sphere charge convergence (:DIS) is
>oscillating but the plane wave convergence is improving DO NOT WORRY, this
>is OK. In my experience, it is only when :PLANE is less than about 0.01
>that the iterations start to converge. I never use -in1new before
>obtaining reasonable convergence of both :DIS and :PLANE.
>
>Caveat: There is a pathalogical case which Peter found once, and I have
>also found in a seperate system. At least in my case it appears to be
>oscillations which can go unstable between some spin-up and spin-dn states
>very close to the Fermi energy. These presumable contain both
>atomic-sphere and plane wave components so a relative scaling is not
>helping enough. If anyone has any ideas about how to handle such a problem
>in terms of scaling let me know off-line.
>
>N.B., testconv -p :PLA works to test the plane wave convergence, but at
>present is not built into the runXYZ scripts but can easily be added.
>
>-----------------------------------------------
>Laurence Marks
>Department of Materials Science and Engineering
>MSE Rm 2036 Cook Hall
>2220 N Campus Drive
>Northwestern University
>Evanston, IL 60201, USA
>Tel: (847) 491-3996 Fax: (847) 491-7820
>email: L - marks @ northwestern . edu
>http://www.numis.northwestern.edu
>-----------------------------------------------
>

= = = = = = = = = = = = = = = = = = = =

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????????liyh
????????lyhua at fudan.edu.cn
??????????2005-03-02

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