[Pw_forum] Convergene of Magnetic moment is very slow

[Giovani Faccin]

Kamal,

The scf will try to optimize the total energy. Once the energy is
optimized, the magnetic moment should stop oscillating.

Each step the program prints this line: "estimated scf accuracy: XXXXX". If
XXXXX is becoming smaller over time, the calculation is converging. If not,
then you can try other beta values, as discussed here:
http://www.quantum-espresso.org/user_guide/node64.html#SECTION000137020000000000000

Just looking at the magnetization before the system gets self-consistent is
pointless, since all kind of values will show up.

A little idea that might help: be sure that you have enough kpoints. 5x5x5
can be too few for many purposes. I'd give it a try with, say, 11x11x11 to
see if the final magnetization (after the scf is concluded) changes.


Best regards,

Giovani M. Faccin
CPPP / UFMS - Brazil



2012/3/2 <ksaha at physics.udel.edu>

> Dear Users,
>
> I am running scf-iterations of a ferrimagnetic yttrium iron garnet (bcc
> primitive cell with 80 atoms) system and find that the convergence of
> magnetic moment is very slow. Can you any suggest me how to accelerate the
> overall convergence? Please see the last a few steps of magmom of the
> 100-scf steps:
>
>     total magnetization       =    78.61 Bohr mag/cell
>     total magnetization       =    78.79 Bohr mag/cell
>     total magnetization       =    78.78 Bohr mag/cell
>     total magnetization       =    78.91 Bohr mag/cell
>     total magnetization       =    79.25 Bohr mag/cell
>     total magnetization       =    79.17 Bohr mag/cell
>     total magnetization       =    79.22 Bohr mag/cell
>     total magnetization       =    79.06 Bohr mag/cell
>     total magnetization       =    79.08 Bohr mag/cell
>     total magnetization       =    79.10 Bohr mag/cell
>     total magnetization       =    79.12 Bohr mag/cell
>     total magnetization       =    79.09 Bohr mag/cell
>     total magnetization       =    79.15 Bohr mag/cell
>     total magnetization       =    79.23 Bohr mag/cell
>     total magnetization       =    79.17 Bohr mag/cell
>     total magnetization       =    79.47 Bohr mag/cell
>     total magnetization       =    79.45 Bohr mag/cell
>     total magnetization       =    79.15 Bohr mag/cell
>     total magnetization       =    81.33 Bohr mag/cell
>     total magnetization       =    82.16 Bohr mag/cell
>     total magnetization       =    82.24 Bohr mag/cell
>     total magnetization       =    82.32 Bohr mag/cell
>     total magnetization       =    82.53 Bohr mag/cell
>     total magnetization       =    84.89 Bohr mag/cell
>     total magnetization       =    82.93 Bohr mag/cell
>     total magnetization       =    78.05 Bohr mag/cell
>     total magnetization       =    84.82 Bohr mag/cell
>     total magnetization       =    84.32 Bohr mag/cell
>     total magnetization       =    84.69 Bohr mag/cell
>     total magnetization       =    85.38 Bohr mag/cell
>     total magnetization       =    87.34 Bohr mag/cell
>
> Also, here is the part of the script which you may want to look at:
>
>  &system
>    ibrav = 3,
>    celldm(1) = 23.24362966,          ! = a, in Bohr
>    nat= 80,
>    ntyp= 3,
>    nspin=2,
>    starting_magnetization(1)=0.0,
>    starting_magnetization(2)=2.60,
>    starting_magnetization(3)=0.0,
>    occupations='smearing',
>    smearing='mp',
>    degauss=0.02,
>    ecutwfc =30,
>    ecutrho =240
>  /
>  &electrons
>    electron_maxstep = 400,
>    diagonalization='david',
>    conv_thr = 1.0e-6,
>    mixing_beta = 0.05,
>    !mixing_ndim = 6
>    mixing_ndim = 10
>  /
> ATOMIC_SPECIES
>  Y   88.90585    Y.pbe-nsp-van.UPF
>  Fe  55.84500    Fe.pbe-sp-van_mit.UPF
>  O   15.99940    O.pbe-van_ak.UPF
> .
> .
> .
> K_POINTS automatic
>  5 5 5  1 1 1
>
> Many thanks for your comments and suggestions,
>
> Regards,
> Kamal
>
> ==========================================================
>  Kamal K. Saha
>  Department of Physics and Astronomy
>  University of Delaware
>  Newark, DE 19716-2570
>  Phone: (302) 831-8519, Fax: (302) 831-1637
>
>  http://web.physics.udel.edu/about/directory/postdoc/kamal-k-saha
> ==========================================================
>
>
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