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

Mon Apr 25 20:56:12 CEST 2011

Hi all,

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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