Re: [QE-users] magnetism in hematite (alpha-Fe2O3)

Yasser Fowad AlWahedi Sat, 07 Apr 2018 09:51:11 -0700

Dear Mostafa

Iron oxides specifically Hematite, Maghemite and Magnetite require using a different approach. For these materials, the proper way to handle them is by using a hubbard potential in a formulation know as DFT+U or LDA+U.

The right hubbard potential for Hematite can be found in the literature. I can send u later an input file for Maghemite.

Probably that's the reason you are facing difficulty in producing experimental results.

Yasser Al Wahedi

Assistant Professor

Khalifa University

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From: Mostafa Youssef

Sent: Saturday, 7 April, 16:53

Subject: [QE-users] magnetism in hematite (alpha-Fe2O3)

To: users@lists.quantum-espresso.org

Dear all

Hematite (alpha-Fe2O3) crystallizes in the corundum structure. The primitive cell is rhombohedral containing 2 formula units, whereas the conventional cell is hexagonal containing 6 formula units. I'm trying to model the antiferromagnetic phase of hematite with spin ordering (+--+) in the primitive cell. Relaxation (or variable cell relaxation) works nicely for the primitive cell and I obtain a reasonable final structure and magnetic moments on iron ions and zero magnetic moment in oxygen ions. This is consistent with literature. Note that all iron ions are equivalent crystallographically and all oxygen ions are crystallographyically. However, when I try to relax (or vc-relax) the corresponding conventional cell, some symmetry breaking occurs and few iron ions develop magnetic moment different than the rest. Additionally some oxygen ions develop magnetic moment as well. The final result is antiferromagnetic still, but of course the structure is not consistent with prior reports and is not consistent with primitive cell calculations. Also the energy/Fe2O3 for the conventional cell is higher than the primitive cell. I tried many things to avoid this strange-looking local minimum such as:

1- Using cg instead of david algorithm.

2- Different starting magnetization

3- Different initial experimentally determined atom positions

4- Different pseudopotentials

5- Applying smearing

6- Gamma-centered vs. shifted k-points

7-Using ibrav = 4 and listing a and c, vs. using ibrav = 0 and providing cell_parameters list

but nothing really seems to work.

Any suggestions are thoughts arevery appreciated. I provide below the input files for both primitive and conventional cells and I'm using version 6.2.1. I also provide the final magnetization of the ions in the conventional cell.

Best Regards,

Mostafa Youssef

AUC - Egypt

# Input file for the primitive cell

&CONTROL

calculation = 'vc-relax' ,

verbosity = 'high' ,

restart_mode = 'from_scratch' ,

prefix='fe2o3' ,

outdir='/data/mostafa/Fe2O3/fix_magnet_strucutre2/scratch/' ,

pseudo_dir = '/home/mostafa/data/Fe2O3/PP' ,

tstress = .true. ,

tprnfor= .true. ,

nstep = 2000 ,

etot_conv_thr = 7.7D-6 ,

forc_conv_thr = 4.0D-5 ,

&SYSTEM

ibrav = 0 ,

nat = 10 ,

ntyp = 3 ,

nbnd = 96 ,

ecutwfc = 90 ,

ecutrho = 1080 ,

nosym =.true.

occupations = 'fixed',

nspin = 2 ,

starting_magnetization(1)=1.0,

starting_magnetization(2)=-1.0,

tot_magnetization = 0

&ELECTRONS

diagonalization='david',

mixing_mode = 'plain' ,

mixing_beta = 0.5,

startingwfc = 'random',

conv_thr = 1.0d-9 ,

&ions

ion_dynamics='bfgs'

&CELL

cell_dynamics = 'bfgs' ,

cell_dofree = 'all',

press_conv_thr = 0.5 , ! This is the default

CELL_PARAMETERS angstrom

5.4200000000000000 0.0000000000000000 0.0000000000000000

3.0870500000000000 4.4549430000000000 0.0000000000000000

3.0870500000000000 1.6166160000000000 4.1512740000000000

ATOMIC_SPECIES

Fe1 55.845 Fe.pbe-spn-rrkjus_psl.0.2.1.UPF

Fe2 55.845 Fe.pbe-spn-rrkjus_psl.0.2.1.UPF

O 15.999 O.pbe-n-rrkjus_psl.0.1.UPF

ATOMIC_POSITIONS crystal

Fe1 0.14500 0.14500 0.14500

Fe1 0.85500 0.85500 0.85500

Fe2 0.35500 0.35500 0.35500

Fe2 0.64500 0.64500 0.64500

O 0.75000 0.45800 0.04200

O 0.95800 0.25000 0.54200

O 0.45800 0.04200 0.75000

O 0.25000 0.54200 0.95800

O 0.04200 0.75000 0.45800

O 0.54200 0.95800 0.25000

K_POINTS automatic

4 4 4 1 1 1

############################################################################

# Conventional cell

############################################################################

&CONTROL

calculation = 'vc-relax' ,

verbosity = 'high' ,

restart_mode = 'from_scratch' ,

prefix='fe2o3' ,

outdir='/data/mostafa/Fe2O3/fix_magnet_conventional_str3_gamma/scratch/' ,

pseudo_dir = '/home/mostafa/data/Fe2O3/PP' ,

tstress = .true. ,

tprnfor= .true. ,

nstep = 2000 ,

etot_conv_thr = 7.7D-6 ,

forc_conv_thr = 4.0D-5 ,

&SYSTEM

ibrav = 0 ,

nat = 30 ,

ntyp = 3 ,

nbnd = 176 ,

ecutwfc = 90 ,

ecutrho = 1080 ,

!!!nosym =.true.

occupations = 'fixed',

nspin = 2 ,

starting_magnetization(1)= 1.0,

starting_magnetization(2)= -1.0,

!!starting_magnetization(3)= 0.0,

tot_magnetization = 0

&ELECTRONS

diagonalization='david',

mixing_mode = 'plain' ,

mixing_beta = 0.5,

startingwfc = 'random',

conv_thr = 1.0d-9 ,

&ions

ion_dynamics='bfgs'

&CELL

cell_dynamics = 'bfgs' ,

cell_dofree = 'all',

press_conv_thr = 0.5 , ! This is the default

CELL_PARAMETERS angstrom

5.0288000107 0.0000000000 0.0000000000

-2.5144000053 4.3550685598 0.0000000000

0.0000000000 0.0000000000 13.7302999496

ATOMIC_SPECIES

Fe1 55.845 Fe.pbe-spn-rrkjus_psl.0.2.1.UPF

Fe2 55.845 Fe.pbe-spn-rrkjus_psl.0.2.1.UPF

O 15.999 O.pbe-n-rrkjus_psl.0.1.UPF

ATOMIC_POSITIONS crystal

Fe1 0.000000000 0.000000000 0.144999996

Fe1 0.000000000 0.000000000 0.855000019

Fe2 0.000000000 0.000000000 0.355000019

Fe2 0.000000000 0.000000000 0.644999981

Fe2 0.666666687 0.333333343 0.478333324

Fe1 0.666666687 0.333333343 0.188333333

Fe2 0.666666687 0.333333343 0.688333333

Fe1 0.666666687 0.333333343 0.978333354

Fe1 0.333333343 0.666666687 0.811666667

Fe2 0.333333343 0.666666687 0.521666646

Fe1 0.333333343 0.666666687 0.021666670

Fe2 0.333333343 0.666666687 0.311666667

O 0.291999996 0.000000000 0.250000000

O 0.708000004 0.000000000 0.750000000

O 0.000000000 0.291999996 0.250000000

O 0.000000000 0.708000004 0.750000000

O 0.708000004 0.708000004 0.250000000

O 0.291999996 0.291999996 0.750000000

O 0.958666682 0.333333343 0.583333313

O 0.374666661 0.333333343 0.083333336

O 0.666666687 0.625333309 0.583333313

O 0.666666687 0.041333336 0.083333336

O 0.374666661 0.041333336 0.583333313

O 0.958666682 0.625333309 0.083333336

O 0.625333309 0.666666687 0.916666687

O 0.041333336 0.666666687 0.416666657

O 0.333333343 0.958666682 0.916666687

O 0.333333343 0.374666661 0.416666657

O 0.041333336 0.374666661 0.916666687

O 0.625333309 0.958666682 0.416666657

K_POINTS automatic

4 4 2 0 0 0

###################################

Final magnetization from vc-relax of the conventional cell

atom: 1 charge: 12.8867 magn: 3.3569 constr: 0.0000

atom: 2 charge: 12.8867 magn: 3.3569 constr: 0.0000

atom: 3 charge: 12.8867 magn: -3.3569 constr: 0.0000

atom: 4 charge: 12.8867 magn: -3.3569 constr: 0.0000

atom: 5 charge: 12.9309 magn: -1.3993 constr: 0.0000

atom: 6 charge: 12.9053 magn: 3.2614 constr: 0.0000

atom: 7 charge: 12.9053 magn: -3.2614 constr: 0.0000

atom: 8 charge: 12.9309 magn: 1.3993 constr: 0.0000

atom: 9 charge: 12.9053 magn: 3.2614 constr: 0.0000

atom: 10 charge: 12.9309 magn: -1.3993 constr: 0.0000

atom: 11 charge: 12.9309 magn: 1.3993 constr: 0.0000

atom: 12 charge: 12.9053 magn: -3.2614 constr: 0.0000

atom: 13 charge: 5.2738 magn: 0.0000 constr: 0.0000

atom: 14 charge: 5.2738 magn: 0.0000 constr: 0.0000

atom: 15 charge: 5.2738 magn: 0.0000 constr: 0.0000

atom: 16 charge: 5.2738 magn: 0.0000 constr: 0.0000

atom: 17 charge: 5.2738 magn: 0.0000 constr: 0.0000

atom: 18 charge: 5.2738 magn: 0.0000 constr: 0.0000

atom: 19 charge: 5.2642 magn: -0.1646 constr: 0.0000

atom: 20 charge: 5.2642 magn: 0.1646 constr: 0.0000

atom: 21 charge: 5.2642 magn: -0.1646 constr: 0.0000

atom: 22 charge: 5.2642 magn: 0.1646 constr: 0.0000

atom: 23 charge: 5.2642 magn: -0.1646 constr: 0.0000

atom: 24 charge: 5.2642 magn: 0.1646 constr: 0.0000

atom: 25 charge: 5.2642 magn: 0.1646 constr: 0.0000

atom: 26 charge: 5.2642 magn: -0.1646 constr: 0.0000

atom: 27 charge: 5.2642 magn: 0.1646 constr: 0.0000

atom: 28 charge: 5.2642 magn: -0.1646 constr: 0.0000

atom: 29 charge: 5.2642 magn: 0.1646 constr: 0.0000

atom: 30 charge: 5.2642 magn: -0.1646 constr: 0.0000

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Re: [QE-users] magnetism in hematite (alpha-Fe2O3)

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