[Pw_forum] Noncollinear magnetization and spin orbit coupling problem on Energy convergence and Spin
Winfred Mulwa
mulwawinfred at gmail.com
Wed Feb 26 12:56:27 CET 2014
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
>
>
>
>
>
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>
--
Mulwa Winfred.
D Phil Student, Computational Material Science Group,
University of Eldoret,
Eldoret, Kenya.
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