[Wien] Ghost band come from large charge fluctuation

Sat Mar 12 02:12:04 CET 2005

Thanks very much to Marks!
There are still some problem not resolved.
As to avoid the large charge fluctuation we set the mixing parameter to 0.000001 and using PRATT 
method, but this can not resolve the problem and we still meet a ghost band in the second iteration.
these are the charge values from  *.scf file.

       CHARGES OF NEW CHARGE DENSITY
:NTO  : TOTAL   INTERSTITIAL CHARGE= 94.6816509
:NTO001: TOTAL   CHARGE IN SPHERE  1 = 29.4424658
:NTO002: TOTAL   CHARGE IN SPHERE  2 = 29.4509322
:NTO003: TOTAL   CHARGE IN SPHERE  3 = 29.4516257
:NTO058: TOTAL   CHARGE IN SPHERE 58 = 31.3918238
:NTO059: TOTAL   CHARGE IN SPHERE 59 = 31.3923983
:NTO060: TOTAL   CHARGE IN SPHERE 60 = 31.3947743

:NEC01: NUCLEAR AND ELECTRONIC CHARGE 1920.000001919.94705   1.00003

       CHARGES OF OLD CHARGE DENSITY
:OTO  : TOTAL   INTERSTITIAL CHARGE= 93.6597633
:OTO001: TOTAL   CHARGE IN SPHERE  1 = 29.5825628
:OTO002: TOTAL   CHARGE IN SPHERE  2 = 29.5924149
:OTO003: TOTAL   CHARGE IN SPHERE  3 = 29.5924481
:OTO058: TOTAL   CHARGE IN SPHERE 58 = 31.1741086
:OTO059: TOTAL   CHARGE IN SPHERE 59 = 31.1741104
:OTO060: TOTAL   CHARGE IN SPHERE 60 = 31.1743886

:NEC02: NUCLEAR AND ELECTRONIC CHARGE 1920.000001916.59208   1.00178    <---------- total charge created from dstart

:DIS  :  CHARGE DISTANCE       0.2025040
       PRATT MIXING SCHEME WITH 0.000

       CHARGES OF MIXED CHARGE DENSITY
:CTO  : TOTAL   INTERSTITIAL CHARGE= 97.0676867
:CTO001: TOTAL   CHARGE IN SPHERE  1 = 29.5825627
:CTO002: TOTAL   CHARGE IN SPHERE  2 = 29.5924149
:CTO003: TOTAL   CHARGE IN SPHERE  3 = 29.5924481
:CTO058: TOTAL   CHARGE IN SPHERE 58 = 31.1741086
:CTO059: TOTAL   CHARGE IN SPHERE 59 = 31.1741104
:CTO060: TOTAL   CHARGE IN SPHERE 60 = 31.1743886

:NEC03: NUCLEAR AND ELECTRONIC CHARGE 1920.000001920.00000   1.00000

Because the mixing value are very small so CTO001 and OTO001 are nearly equal, this is correct.
But if we look at the value of ": TOTAL   INTERSTITIAL CHARGE" it still fluctuated so much, 
from 93.6597633 to 97.0676867, this maybe the reason of ghost bands. I am so surprise to it.
Does the mixing parameter have no influnce to this value?
And I find the total charge value not correct which created from dstart.

>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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　　　　　　　　致
礼！

　　　　　　　　liyh
　　　　　　　　lyhua at fudan.edu.cn
　　　　　　　　　　2005-03-10