[Wien] Problems with convergence with LDA+U calculations including spin-orbit coupling

[Laurence Marks]

As Peter said, do NOT simply reduce the greed, it does not work the
same as it does in PP calculations.

More to the point, you/we need more information to know what is going
on. Assuming that you are using the latest version (or similar) then

grep -e :DIR -e GREED -e :FRMS -e :ENE -e :CHARG -e PRATT -e :DIS -e
"MIXING SC" -e PLANE *.scf  | tail -40

will give more information and what is really going on...

On Mon, Apr 25, 2011 at 2:21 PM, Peter Blaha
<pblaha at theochem.tuwien.ac.at> wrote:
> The convergence behaviour is not very good, but it is not too bad either.
>
> Check also :MMT or some :MMI0xx
>
> For more complicated cases (metallic ??) it is well possible that one needs
> more
> than 40 iterations. Thus my suggestion is to keep going and submit another
> job.
>
> Sometimes it is better to keep the history (use -NI switch), sometimes it
> can also
> be better to remove the history (rm *.broy*; which will be done
> automatically when
> -NI is not supplied).
>
> The mixing parameter has little importance with MSEC1, but still, a too
> small mixing
> can lead to too small steps and thus "pseudoconvergence" (this simply means,
> that so
> little new density is mixed, that eg. the total energy is not changing and
> one thinks
> the calculation is converged).
>
> PRATT is most likely "useless" for your problem.
>
> In LDA+U calculations it is easily possible to reach different states
> (different
> orbital occupations), which are stable and local minima. Once you have
> reached
> convergence, there is never a guarantee that this is the groundstate and
> really
> has the lowest energy.
> The suggested procedure in the UG is NOT ALWAYS leading to the lowest state,
> but often it will do.
>
>
>> I have searched the list but I'm a bit confused with the posts, so I'll
>> pose my questions here.
>>
>> I am running LDA+U with and without spin-orbit coupling for a structure in
>> a cell with the following cell parameters (Bohr):
>>
>> P   LATTICE,NONEQUIV.ATOMS: 14127_P4/mbm
>> MODE OF CALC=RELA
>>  10.353171 10.353171 43.972470 90.000000 90.000000 90.000000
>>
>> and a cell sampling of 12x12x3, which gives 432 points in the BZ, 42 in
>> the IBZ. My RKMAX is 8 - it was necessary to go to such high values to
>> converge the spin moment of
>> the system, as well as the energy down to 1 mRy. I followed the procedure
>> stated in the manual: started with the LSDA calculation, then included
>> spin-orbit coupling and now
>> I am including the U gradually (well, at this point, just trying to...). I
>> have to get to U=4 eV, so I'm growing it in steps of 1 eV.
>>
>> Convergence was very good for the LSDA+U calculations without SOC, and
>> they have finished, already (that is, I have already gotten to the 4 eV in
>> U). However, I am having
>> problems converging the scf, with the charge and energy distances (as
>> obtained by grep convergence case.dayfile) oscillating, and never attaining
>> convergence, which I set
>> to ec=0.00001 and cc=0.0001 (the numbers are appended by the end of this
>> message). More than 40 SCF steps have passed.
>>
>> Usually, in pseudopotential calculations, one possible solution is to
>> decrease the mixing weight of the charge densities for the following SCF
>> step, and the other is to
>> increase the smearing temperature. I would like to tweak with the mixing
>> rather than increasing the temperature, if possible, because from my
>> experience, increasing the
>> temperature can sometimes lead to a non-magnetic state. However, I see
>> from the mailing list that (at least in LAPW calculations), too small a
>> mixing can lead to
>> pseudo-convergence - which I don't understand what is. So, my questions
>> are the following:
>>
>> 1) What is the best thing to do to make my calculation converge: increase
>> the mixing, or to diminish it? Should I change the mixing for MSEC1, and if
>> so, by which amount?
>> Or, would it be good to change to PRATT, instead? I am quite lost with
>> regards to that.
>> 2) Would the application of SOC to the already converged LSDA+U
>> calculation yield too different results from starting from a converged
>> LSDA+SOC with later inclusion of U?
>> 3) What is the pseudo-convergence mentioned in previous emails in the
>> list?
>>
>> Of course, I will gladly provide more information, if needed.
>>
>> Best regards,
>>
>> Marcos
>> Universidad de Cantabria, Spain
>>
>> =======================================
>>
>> Convergence of energy and charge distances:
>>
>> :ENERGY convergence:  0 0.00001 .0002941150000000
>> :CHARGE convergence:  0 0.0001 .0088826
>> :ENERGY convergence:  0 0.00001 .0000916950000000
>> :CHARGE convergence:  0 0.0001 .0085946
>> :ENERGY convergence:  0 0.00001 .0000428400000000
>> :CHARGE convergence:  0 0.0001 .0112915
>> :ENERGY convergence:  0 0.00001 .0001772500000000
>> :CHARGE convergence:  0 0.0001 .0113780
>> :ENERGY convergence:  0 0.00001 .0002456850000000
>> :CHARGE convergence:  0 0.0001 .0104415
>> :ENERGY convergence:  0 0.00001 .0001420300000000
>> :CHARGE convergence:  0 0.0001 .0083852
>> :ENERGY convergence:  0 0.00001 .0000500150000000
>> :CHARGE convergence:  0 0.0001 .0084675
>> :ENERGY convergence:  0 0.00001 .0001809700000000
>> :CHARGE convergence:  0 0.0001 .0134776
>> :ENERGY convergence:  0 0.00001 .0001993400000000
>> :CHARGE convergence:  0 0.0001 .0112308
>> :ENERGY convergence:  0 0.00001 .0002392700000000
>> :CHARGE convergence:  0 0.0001 .0104208
>> :ENERGY convergence:  0 0.00001 .0002088150000000
>> :CHARGE convergence:  0 0.0001 .0069138
>> :ENERGY convergence:  0 0.00001 .0001630050000000
>> :CHARGE convergence:  0 0.0001 .0109876
>> :ENERGY convergence:  0 0.00001 .0002176700000000
>> :CHARGE convergence:  0 0.0001 .0012609
>> :ENERGY convergence:  0 0.00001 .0001806300000000
>> :CHARGE convergence:  0 0.0001 .0042825
>> :ENERGY convergence:  0 0.00001 .0000720450000000
>> :CHARGE convergence:  0 0.0001 .0045301
>> :ENERGY convergence:  0 0.00001 .0000129050000000
>> :CHARGE convergence:  0 0.0001 .0011304
>> :ENERGY convergence:  0 0.00001 .0002283150000000
>> :CHARGE convergence:  0 0.0001 .0047456
>> :ENERGY convergence:  0 0.00001 .0003098100000000
>> :CHARGE convergence:  0 0.0001 .0100820
>> :ENERGY convergence:  0 0.00001 .0003708750000000
>> :CHARGE convergence:  0 0.0001 .0087276
>> :ENERGY convergence:  0 0.00001 .0000788950000000
>> :CHARGE convergence:  0 0.0001 .0090876
>> :ENERGY convergence:  0 0.00001 .0000849050000000
>> :CHARGE convergence:  0 0.0001 .0093747
>> :ENERGY convergence:  0 0.00001 .0000842350000000
>> :CHARGE convergence:  0 0.0001 .0079561
>> :ENERGY convergence:  0 0.00001 .0000553500000000
>> :CHARGE convergence:  0 0.0001 .0122027
>> :ENERGY convergence:  0 0.00001 .0000434050000000
>> :CHARGE convergence:  0 0.0001 .0109352
>> :ENERGY convergence:  0 0.00001 .0000227750000000
>> :CHARGE convergence:  0 0.0001 .0122136
>> :ENERGY convergence:  0 0.00001 .0000194300000000
>> :CHARGE convergence:  0 0.0001 .0121261
>> :ENERGY convergence:  0 0.00001 .0000292700000000
>> :CHARGE convergence:  0 0.0001 .0131197
>> :ENERGY convergence:  0 0.00001 .0000360650000000
>> :CHARGE convergence:  0 0.0001 .0110031
>> :ENERGY convergence:  0 0.00001 .0000300950000000
>> :CHARGE convergence:  0 0.0001 .0115123
>> :ENERGY convergence:  0 0.00001 .0000323600000000
>> :CHARGE convergence:  0 0.0001 .0099887
>> :ENERGY convergence:  0 0.00001 .0000147550000000
>> :CHARGE convergence:  0 0.0001 .0110331
>> :ENERGY convergence:  0 0.00001 .0001196200000000
>> :CHARGE convergence:  0 0.0001 .0005253
>>
>>
>>
>> _______________________________________________
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>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
> --
> -----------------------------------------
> Peter Blaha
> Inst. Materials Chemistry, TU Vienna
> Getreidemarkt 9, A-1060 Vienna, Austria
> Tel: +43-1-5880115671
> Fax: +43-1-5880115698
> email: pblaha at theochem.tuwien.ac.at
> -----------------------------------------
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>



-- 
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/
Research is to see what everybody else has seen, and to think what
nobody else has thought
Albert Szent-Gyorgi