[Pw_forum] Noncollinear magnetization and spin orbit coupling problem on Energy convergence and Spin

Xiao Shi xiaos at Princeton.EDU
Mon Mar 3 20:25:01 CET 2014


Hi Paolo

For the system without O2
If I turned on spin polarization by giving a very small starting spin like 0.0001.
The strong anti-ferromagnetic and not convergence also happens. (sometimes in the first scf cycle, sometimes after several steps of geometry optimization).
Where the simple Bi2Se3 system should have no spin polarization.

PS: The spin polarization only shows in momentum space where the spin and momuntum direction are locked perpendicular to each other. However in real space, there should be no spin polarization.

Best
Xiao Shi
Department of Chemistry
Princeton University


On  Mon, 03 Mar 2014 10:47:42, Paolo Giannozzi wrote
>What happens without the O2 molecule? P.
>
>On Sat, 2014-03-01 at 19:30 +0000, Xiao Shi wrote:
>> Hi Mulwa and other PW users
>>
>>
>>
>>
>> Thanks for your advise. However, the same problem still happens.
>>
>>
>> Has anyone met this kind of situation before? I'm wondering if this is
>> the problem of the system or I didn't set the correct parameters.
>>
>>
>>
>>
>> On Wed, 26 Feb 2014 2:56pm  Winfred Mulwa <mulwawinfred at gmail.com>
>> wrote
>>
>>
>> >Try to set  conv_thr = 1.0 d -4 in the namelist electrons
>> >On Tue, Feb 25, 2014 at 11:41 PM, Xiao Shi <xiaos at princeton.edu>
>> wrote:
>> >
>> >>  Dear PW users
>> >>
>> >>  I'm doing calculations on Bi2Se3 system and get some problem with
>> the
>> >> magnetization of this system.
>> >> As Bi2Se3 is a topological insulator, I need large spin orbit
>> coupling
>> >> effect which means I need to do noncollinear calculation.
>> >>
>> >>  After adding O2 molecule on the surface, I did spin polarization
>> >> calculation where the energy doesn't converge and the system goes
>> into
>> >> anti-ferromagnetic like shown below:
>> >>
>> >>
>> >>       total energy              =   -5045.36386241 Ry
>> >>      Harris-Foulkes estimate   =   -5045.36391863 Ry
> >>>      estimated scf accuracy    <       0.00001751 Ry
> >>>
> >> >      total magnetization       =    -0.00     0.00     2.00 Bohr
>> mag/cell
> >>>      absolute magnetization    =     3.42 Bohr mag/cell
> >>>
> >>>
> >>>  If I continue for more steps, it will grows into very large
> >>> anti-ferromagnetic like 20 Bohr mag/cell for absolute magnetization
>> which
> >>> is unphysical. The O2 I placed is far away from the surface and
>> there
> >>> shouldn't be any spin polarization for pristine surface in reality.
> >Also
> >>> the total energy doesn't change monotonically.
> >>>
> >>>
> >> > The input file is listed below:
> >> >This is a supercell system of Bi2Se3 with 2*2 in the hcp lattice
> >and there
> >> >are 15 layers of atom for the slab with vacuum larger than 20ans
> >(O2 is at
> >> >least 10ans away from the slab)
> >>>
> >>>   &system
> >> >   ibrav=4,
> >>>    celldm(1)=15.992,
> >>>    celldm(3)=6.555356882,
> >>>    nat=62,
> >>>    ntyp=3,
>> >>    ecutwfc=30.0,
>> >>    ecutrho=300.0,
>> >>    occupations='smearing',
>> >>    degauss=0.002,
>> >>    noncolin=.true.,
>> >>    lspinorb=.true.,
>> >>    starting_magnetization(1)=-0.001,
> >>>    starting_magnetization(2)=0.001,
> >>>    starting_magnetization(3)=0.5,
>> >>    london=.true.
> >>>    starting_spin_angle=.true.
> >>>    nosym=.true.
> >>>  /
> >>>  &electrons
> >>>   mixing_beta=0.2
> >>>
> >>>   ATOMIC_SPECIES
> >>>  Bi 208.98 Bi.rel-pbe-dn-rrkjus.UPF
> >>>  Se 78.96 Se.rel-pbe-n-rrkjus_psl.0.2.UPF
> >>>  O 16.00 O.rel-pbe-n-rrkjus_psl.0.1.UPF
> >>> ATOMIC_POSITIONS {crystal}
> >>> O       0.582808125     0.518307602     0.030071968
> >>> O       0.438796581     0.511316952     0.033700923
>> >> Se      0.333363441     0.666726883     0.270506612
>> >> Se      0.333363312     0.166681597     0.270506668
>> >> Se      0.833409077     0.166681597     0.270506668
>> >> Se      0.833408961     0.666727129     0.270506668
> >>> Bi      4E-16   3E-16   0.298539365
> >>> Bi      8.34671E-08     0.500045262     0.298539398
>> >> Bi      0.500045295     -2.00018E-07    0.298539398
>> >> Bi      0.500045179     0.500045262     0.298539398
> >>> Se      0.666727117     0.333363441     0.332477455
> >>> Se      0.166681746     0.333363493     0.332477478
>> >> Se      0.166681629     0.833408578     0.332477478
>> >> Se      0.666726948     0.833408578     0.332477478
> >>> Bi      0.333363498     0.166681691     0.366247219
> >>> Bi      0.833408983     0.166681691     0.366247219
>> >> Bi      0.833408867     0.666726943     0.366247219
>> >> Bi      0.333363441     0.666726883     0.366247266
>> >> Se      3.44477E-08     0.500045237     0.394371017
>> >> Se      0.50004532      -1.51013E-07    0.394371017
>> >> Se      0.500045204     0.500045237     0.394371017
>> >> Se      5E-16   3E-16   0.394371148
>> >> Se      0.166681762     0.333363525     0.438001919
>> >> Se      0.166681646     0.833408563     0.438001919
>> >> Se      0.666726916     0.833408563     0.438001919
>> >> Se      0.666727117     0.333363441     0.438001924
>> >> Bi      0.333363644     0.166681764     0.466101291
>> >> Bi      0.83340891      0.166681764     0.466101291
>> >> Bi      0.833408794     0.666726797     0.466101291
>> >> Bi      0.333363441     0.666726883     0.466101294
>> >> Se      5E-16   4E-16   0.5
>> >> Se      -1.1658E-07     0.500045162     0.5
>> >> Se      0.500045395     5E-16   0.5
>> >> Se      0.500045279     0.500045162     0.5
> >>> Bi      0.666727117     0.333363441     0.533898706
> >>> Bi      0.166681764     0.333363527     0.533898709
>> >> Bi      0.166681648     0.83340856      0.533898709
>> >>  Bi      0.666726914     0.83340856      0.533898709
> >>> Se      0.333363441     0.666726883     0.561998076
> >>> Se      0.333363642     0.166681762     0.561998081
>> >> Se      0.833408912     0.166681762     0.561998081
>> >> Se      0.833408796     0.666726799     0.561998081
>> >> Se      7E-16   5E-16   0.605628852
>> >> Se      -2.67539E-07    0.500045087     0.605628983
>> >> Se      0.50004547      1.51013E-07     0.605628983
>> >> Se      0.500045354     0.500045087     0.605628983
>> >> Bi      0.666727117     0.333363441     0.633752734
>> >> Bi      0.166681691     0.333363381     0.633752781
>> >> Bi      0.166681575     0.833408634     0.633752781
>> >> Bi      0.66672706      0.833408634     0.633752781
>> >> Se      0.33336361      0.166681746     0.667522522
>> >> Se      0.833408928     0.166681746     0.667522522
>> >> Se      0.833408812     0.666726831     0.667522522
>> >> Se      0.333363441     0.666726883     0.667522545
> >>> Bi      -3.16627E-07    0.500045062     0.701460602
> >>> Bi      0.500045495     2.00018E-07     0.701460602
> >>> Bi      0.500045379     0.500045062     0.701460602
> >>> Bi      7E-16   6E-16   0.701460635
> >>> Se      0.166681597     0.333363195     0.729493332
> >>> Se      0.166681481     0.833408728     0.729493332
> >>> Se      0.666727246     0.833408728     0.729493332
> >>> Se      0.666727117     0.333363441     0.729493388
> >>> K_POINTS {automatic}
> >>> 3 3 1 0 0 0
> >>>
> >>>
> >>>  I wonder has any meet this problem before and can give me some
> >>> suggestion on it?
> >>>
> >>>  PS: I've tried increase degauss to 0.05Ryd and decrease
>>>> mixing_beta to
> >>> 0.05 which doesn't help
> >>>
> >>>  Best Regard
> >>>
>> >>  Xiao Shi
>> >> Department of Chemistry
> >>> Princeton University
> >>>
>> >>
> >>>
> >>>
> >>>
> >> >_______________________________________________
>> >> Pw_forum mailing list
>> >> Pw_forum at pwscf.org
> >>> http://pwscf.org/mailman/listinfo/pw_forum
> >>>
> >>
> >>
> >>
> >>--
> >>Mulwa Winfred.
> >>D Phil Student, Computational Material Science Group,
> >>University of Eldoret,
> >>Eldoret, Kenya.
> >
> >
> >
> >
> >
> >
> >Best
> >Xiao Shi
> >Department of Chemistry
> >Princeton University
> >
> >
> >_______________________________________________
> >Pw_forum mailing list
> >Pw_forum at pwscf.org
> >http://pwscf.org/mailman/listinfo/pw_forum
>
>--
> Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222

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