[Pw_forum] non-collinear calculations in QE (5.0.1)
Hanghui Chen
chenhanghuipwscf at gmail.com
Sat Feb 4 07:28:07 CET 2017
Dear QE developers,
I have performed some non-collinear calculations on a double
perovskite Sr2TiTcO6 using QE 5.0.1 and found some confusing results. Your
help is greatly appreciated.
The double perovskite Sr2TiTcO6 has a cubic symmetry where Tc has a
S=3/2 spin and Ti is non-magnetic. Both Tc and Ti ions occupy on a
face-centered-cubic (fcc) lattice. Therefore non-collinear magnetism is
possible on Tc ions.
I used the cubic structure and compared two calculations: one has a
collinear antiferromagnetic (AFM) ordering and the other has a
non-collinear AFM ordering. Both input files are attached. The calculation
shows that the non-collinear AFM state is 108 meV/per-40-atom-cell more
stable than the collinear AFM state. This energy difference is very large
(typical magnetic anisotropy energy is about 0.1 meV/per atom).
More importantly, since the cubic system can be described by a
nearest-neighbor classic Heisenberg model H = \sum_{i<j} Si\cdoc Sj. We can
show explicitly (with some algebra) that the collinear AFM and noncollinear
AFM should have exactly the same energy.
Note that in my calculations, all the pseudo-potentials only have
scalar relativistic correction, so there is no spin-orbit interaction.
Therefore there is no Dzyaloshinskii-Moriya interaction or magnetic
anisotropy energy in the spin Hamiltonian. The only relevant term is the
Heisenberg interaction, which predicts degeneracy of the two AFM states.
I do believe that the implementation of non-collinear calculation in
QE is correct. But I am confused by what physical interaction (which is
included in DFT calculations) causes the large energy splitting between the
collinear and non-collinear AFM states in my calculations.
Your insightful comments are greatly appreciated.
Thank you very much.
Dr. Hanghui Chen
Assistant Professor of Physics
Department of Physics
New York University Shanghai and New York University
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&CONTROL
calculation='scf'
wf_collect=.true.
pseudo_dir = '~/psp'
outdir='./'
wfcdir='./'
prefix='Sr2TiTcO6-001AF'
disk_io='low'
verbosity='high'
tprnfor = .true.
tstress = .true.
dt=80.D0
nstep = 100
/
&SYSTEM
ibrav = 0
nat = 40
ntyp = 7
ecutwfc = 40.0
ecutrho = 320.0
occupations = 'smearing'
smearing = 'mp'
degauss = 0.005
noncolin = .true.
report = 1
starting_magnetization(3) = 1.d0
starting_magnetization(4) = 1.d0
starting_magnetization(5) = -1.d0
starting_magnetization(6) = -1.d0
angle1(3) = 0.0
angle2(3) = 0.0
angle1(4) = 0.0
angle2(4) = 0.0
angle1(5) = 0.0
angle2(5) = 0.0
angle1(6) = 0.0
angle2(6) = 0.0
/
&ELECTRONS
diagonalization='david'
mixing_beta = 0.2d0
diago_david_ndim = 4
mixing_mode= 'local-TF'
electron_maxstep = 1000
startingpot = 'atomic'
conv_thr= 1.d-7
/
&IONS
ion_dynamics = 'bfgs'
phase_space = 'full'
trust_radius_max = 0.4
trust_radius_ini = 0.2
/
&CELL
cell_dynamics = 'bfgs'
/
ATOMIC_SPECIES
Sr 87.62 sr_pbe_v1.uspp.F.UPF
Ti 47.87 ti_pbe_v1.4.uspp.F.UPF
Tc1 98.00 tc_pbe_v1.uspp.F.UPF
Tc2 98.00 tc_pbe_v1.uspp.F.UPF
Tc3 98.00 tc_pbe_v1.uspp.F.UPF
Tc4 98.00 tc_pbe_v1.uspp.F.UPF
O 16.00 o_pbe_v1.2.uspp.F.UPF
ATOMIC_POSITIONS crystal
Sr 0.000000 0.000000 0
Sr 0.500000 0.000000 0
Sr 0.000000 0.500000 0
Sr 0.500000 0.500000 0
Sr 0.000000 0.000000 0.5
Sr 0.500000 0.000000 0.5
Sr 0.000000 0.500000 0.5
Sr 0.500000 0.500000 0.5
Ti 0.250000 0.250000 0.25
Ti 0.750000 0.750000 0.25
Ti 0.250000 0.750000 0.75
Ti 0.750000 0.250000 0.75
Tc1 0.250000 0.750000 0.25
Tc2 0.750000 0.250000 0.25
Tc3 0.250000 0.250000 0.75
Tc4 0.750000 0.750000 0.75
O 0.250000 0.250000 0
O 0.250000 0.750000 0
O 0.750000 0.250000 0
O 0.750000 0.750000 0
O 0.250000 0.000000 0.25
O 0.750000 0.000000 0.25
O 0.000000 0.250000 0.25
O 0.500000 0.250000 0.25
O 0.250000 0.500000 0.25
O 0.750000 0.500000 0.25
O 0.000000 0.750000 0.25
O 0.500000 0.750000 0.25
O 0.250000 0.250000 0.5
O 0.250000 0.750000 0.5
O 0.750000 0.250000 0.5
O 0.750000 0.750000 0.5
O 0.250000 0.000000 0.75
O 0.750000 0.000000 0.75
O 0.000000 0.250000 0.75
O 0.500000 0.250000 0.75
O 0.250000 0.500000 0.75
O 0.750000 0.500000 0.75
O 0.000000 0.750000 0.75
O 0.500000 0.750000 0.75
K_POINTS {automatic}
6 6 6 0 0 0
CELL_PARAMETERS bohr
15.00000000000000000 0.00000000000000000 0.0000000000000000
0.00000000000000000 15.00000000000000000 0.0000000000000000
0.00000000000000000 0.00000000000000000 15.0000000000000000
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&CONTROL
calculation='scf'
wf_collect=.true.
pseudo_dir = '~/psp'
outdir='./'
wfcdir='./'
prefix='Sr2TiTcO6-two'
disk_io='low'
verbosity='high'
tprnfor = .true.
tstress = .true.
dt=80.D0
nstep = 100
/
&SYSTEM
ibrav = 0
nat = 40
ntyp = 7
ecutwfc = 40.0
ecutrho = 320.0
occupations = 'smearing'
smearing = 'mp'
degauss = 0.005
noncolin = .true.
report = 1
starting_magnetization(3) = 1.d0
starting_magnetization(4) = 1.d0
starting_magnetization(5) = 1.d0
starting_magnetization(6) = 1.d0
angle1(3) = 90.0
angle2(3) = 135.0
angle1(4) = 90.0
angle2(4) = 315.0
angle1(5) = 90.0
angle2(5) = 225.0
angle1(6) = 90.0
angle2(6) = 45.0
/
&ELECTRONS
diagonalization='david'
mixing_beta = 0.2d0
diago_david_ndim = 4
mixing_mode= 'local-TF'
electron_maxstep = 1000
startingpot = 'atomic'
conv_thr= 1.d-7
/
&IONS
ion_dynamics = 'bfgs'
phase_space = 'full'
trust_radius_max = 0.4
trust_radius_ini = 0.2
/
&CELL
cell_dynamics = 'bfgs'
/
ATOMIC_SPECIES
Sr 87.62 sr_pbe_v1.uspp.F.UPF
Ti 47.87 ti_pbe_v1.4.uspp.F.UPF
Tc1 98.00 tc_pbe_v1.uspp.F.UPF
Tc2 98.00 tc_pbe_v1.uspp.F.UPF
Tc3 98.00 tc_pbe_v1.uspp.F.UPF
Tc4 98.00 tc_pbe_v1.uspp.F.UPF
O 16.00 o_pbe_v1.2.uspp.F.UPF
ATOMIC_POSITIONS crystal
Sr 0.000000 0.000000 0
Sr 0.500000 0.000000 0
Sr 0.000000 0.500000 0
Sr 0.500000 0.500000 0
Sr 0.000000 0.000000 0.5
Sr 0.500000 0.000000 0.5
Sr 0.000000 0.500000 0.5
Sr 0.500000 0.500000 0.5
Ti 0.250000 0.250000 0.25
Ti 0.750000 0.750000 0.25
Ti 0.250000 0.750000 0.75
Ti 0.750000 0.250000 0.75
Tc1 0.250000 0.750000 0.25
Tc2 0.750000 0.250000 0.25
Tc3 0.250000 0.250000 0.75
Tc4 0.750000 0.750000 0.75
O 0.250000 0.250000 0
O 0.250000 0.750000 0
O 0.750000 0.250000 0
O 0.750000 0.750000 0
O 0.250000 0.000000 0.25
O 0.750000 0.000000 0.25
O 0.000000 0.250000 0.25
O 0.500000 0.250000 0.25
O 0.250000 0.500000 0.25
O 0.750000 0.500000 0.25
O 0.000000 0.750000 0.25
O 0.500000 0.750000 0.25
O 0.250000 0.250000 0.5
O 0.250000 0.750000 0.5
O 0.750000 0.250000 0.5
O 0.750000 0.750000 0.5
O 0.250000 0.000000 0.75
O 0.750000 0.000000 0.75
O 0.000000 0.250000 0.75
O 0.500000 0.250000 0.75
O 0.250000 0.500000 0.75
O 0.750000 0.500000 0.75
O 0.000000 0.750000 0.75
O 0.500000 0.750000 0.75
K_POINTS {automatic}
6 6 6 0 0 0
CELL_PARAMETERS bohr
15.00000000000000000 0.00000000000000000 0.0000000000000000
0.00000000000000000 15.00000000000000000 0.0000000000000000
0.00000000000000000 0.00000000000000000 15.0000000000000000
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