[Wien] Large charge fluctuation in hybrid calculations

[Laurence Marks]

Assuming that you are using MSEC1, the fundamental reason that
"standard tricks" don't work is, simply, that these tricks don't work
with MSEC1! (In fact they don't really work the way people think even
with BROYD, and never have, although they might with PRATT.)

The normal reason why a calculation does not converge is because the
physics is badly posed in the model being used. You say that the
problem occurs even in cycle 1 for NSO calculations, so is not related
to -so or -eece. I would go back and look very carefully at how the
8-layer model is setup; are the atoms right, do you have inadequate
k-points, is there something wrong in the symmetry? (99% certain that
you will find something).

N.B., I would be very cautious (skeptical) about applying a on-site
hybrid method to a metal. This may be both incorrect physics and the
problem may be unfeasible, i.e. there may be not self-consistent
solution. (Nothing in fact says that a self-consistent solution has to
exist!)

2009/8/11 Atta-fynn, Raymond <attafynn at uta.edu>:
> Dear Users,
>
> I am performing non-magnetic calculations on a metal slab using hybrid DFT
> (with TEMP smearing). I have been able to converge 1-7 layers and 9-layer
> thick slabs with no serious problems. For some reason the 8-layer slab does
> not want to converge. The charge density oscillates with large
> amplitudes and eventually the job crashes. Calculations were performed the
> standard way:
>
> runsp_c_lapw -ec 0.00001 -cc 0.001 -i 300 -p
> runsp_c_lapw -ec 0.00001 -cc 0.001 -i 300 -p -so
> runsp_c_lapw -ec 0.00001 -cc 0.001 -i 300 -p -so -eece
>
> The problem begins in step 1 (NSO calculations). I've pulled all  the
> standard tricks (reduce mixing, etc.) but the problem will just not go away.
> The first few cycles for the charge distance looks like:
>
> :DIS  :  CHARGE DISTANCE       ( 3.0623129 for atom    2 spin 2)
> 4.8323633
> :DIS  :  CHARGE DISTANCE       ( 3.7525968 for atom    8 spin 2)
> 4.8109130
> :DIS  :  CHARGE DISTANCE       ( 4.5335108 for atom    4 spin 2)
> 4.7597241
> :DIS  :  CHARGE DISTANCE       ( 5.1545071 for atom    8 spin 2)
> 4.9702637
> :DIS  :  CHARGE DISTANCE       ( 5.0675077 for atom    1 spin 2)
> 4.8569369
> :DIS  :  CHARGE DISTANCE       ( 4.9684119 for atom    1 spin 2)
> 4.7391195
> :DIS  :  CHARGE DISTANCE       ( 4.3727780 for atom    1 spin 2)
> 4.3237943
> :DIS  :  CHARGE DISTANCE       ( 3.7769948 for atom    4 spin 2)
> 4.8503262
> :DIS  :  CHARGE DISTANCE       ( 3.3436987 for atom    4 spin 2)
> 3.8495739
> :DIS  :  CHARGE DISTANCE       ( 3.2228522 for atom    1 spin 2)
> 5.1590833
> :DIS  :  CHARGE DISTANCE       ( 2.7148248 for atom    7 spin 2)
> 3.7982418
> :DIS  :  CHARGE DISTANCE       ( 3.3313579 for atom    7 spin 2)
> 4.5302253
> :DIS  :  CHARGE DISTANCE       ( 3.3598285 for atom    4 spin 2)
> 5.0925813
> :DIS  :  CHARGE DISTANCE       ( 2.9529033 for atom    4 spin 2)
> 5.2109088
> :DIS  :  CHARGE DISTANCE       ( 3.3483133 for atom    4 spin 2)
> 5.0412665
> :DIS  :  CHARGE DISTANCE       ( 2.9641391 for atom    7 spin 2)
> 4.8027516
> :DIS  :  CHARGE DISTANCE       ( 3.1663445 for atom    4 spin 2)
> 4.7292585
> :DIS  :  CHARGE DISTANCE       ( 3.2054421 for atom    5 spin 2)
> 3.9307946
> :DIS  :  CHARGE DISTANCE       ( 3.1672886 for atom    5 spin 2)
> 4.4866535
> :DIS  :  CHARGE DISTANCE       ( 3.2654575 for atom    1 spin 2)
> 5.0048377
> :DIS  :  CHARGE DISTANCE       ( 3.1100926 for atom    5 spin 2)
> 4.2558609
> Any suggestions would be appreciated.
>
> Thank you.
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>



-- 
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
Web: www.numis.northwestern.edu
Chair, Commission on Electron Crystallography of IUCR
www.numis.northwestern.edu/
Electron crystallography is the branch of science that uses electron
scattering to study the structure of matter.