Quasiparticle Self-consistent GW Study of LSMO and future studies

1
Quasiparticle Self-consistent GW Study of LSMO
and future studies

• Hiori Kino

Half-metal Important materials for
spin-electronics Future targets Semiconductor
Impurity problem Antiferromagnetic Mott
insulators positions of oxigen levels
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GW method first-principles (no parameter),
correlation RPA-level
LDA
GWA
(RPA, without vertex correction)
(use only the diagonal self-energy)



Bare Exchange and Correlated parts
made of and
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QPscGWquasiparticle self-consistent GW
one-body potential
1. Neglect frequency dependence of S(w) 2. DS0,
when self-consistency is achieved.
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Merits of QPscGW
No Z factor, easy to analyze QP dispersion, full
k-path ...
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Half-metal --- application
DOS
?
?
?
?
Half-metal
?
EF
?
Applications

• Spin valve --- MRAM
• Spin OLED (organic light emitting diode)

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Basic Idea
too simple...
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Spin valve --- MRAM
Alq8-hydroxyquinoline aluminium
-30
Xiong et al., Nature 427, 821 (2004).
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Spin OLED (organic light emitting
diode)---Organic EL (electroluminescence)
Change luminescence efficiency
luminescence
phosphorescence
hn
hn
L1
(slow)
L
T1
S0
S1

• Organic semiconductor
• small Z small L?S coupling
• long spin life time

0
semiconductor
E.g. Davis and Bussmann, JAP 93, 7358 (2003).
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La0.7Sr0.3MnO3, (La0.7Ba0.3MnO3,La0.7Ca0.3MnO3)
LaMnO3 collosal magnetoresistance oxides a
strongly correlated system (intrinsic
ramdomness) In theories LSDA nonzero DOS at EF
in minority spin component In experiments, many
experiments spin polarization 35-100
In this study, calculate La0.7Sr0.3MnO3 beyond
LSDA. estimate a band gap in the GW
approximation.
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Experimental results
For the Minority spin state
Non-zero DOS at EF partially spin-polarized Andr
eev reflection, Soulen Jr. et al., tunnel
junction, Lu et al., Worledge et al., Sun et
al., residual resistivity, Nadgomy et al.
(bulk) Zero DOS at EFfully spin-polarized XPS,
Park et al. resistivity, Zhao et al.
(bulk) tunnel, Wei et al. (bulk)
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e.g. GW improves bandgaps
Ionization energy
L. Hedin, J. Phys. Condens. Matter 11,R489(1999)
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LSDA results of La0.7Ba0.3MnO3

• LMTO-ASA
• virtual crystal approx.

La
O
Majority Mn eg lt- Fermi level Minority Mn t2g lt-
Fermi level
Mn
Pm-3m
La 4f
Mn eg
Mn eg
Mn t2g
Mn t2g
Spin moment3.55mB
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fp-LMTO calculation
Majority spin
La 4f
More accurate dispersion at higher energies
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fp-LMTO
Double Hankel
O3s
Minimum basis
La7s
O3p
La 5p(semicore)
La6d
Mn 5s
Mn 5p
Mn4d
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1st iteration GW result
GW calculation 6x6x6 (20 irreducible) k-points,
100eV
Not easy to see what happens from the figure
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QPscGW result
GW calculation 6x6x6 (20 irreducible) k-points,
100eV
Spin moment3.70mB (fully polarized)
Minority spin, conduction bottom-EF0.9eV
(Previous result, conduction bottom-EF2eV)
La 4f12eV, c.f., exp.(inverse photoemission)
8eV (Is screening insufficient?)
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Effects of Mn potential distribution due to
random La/Ca distribution
La 2/3 Ca 1/3

• La2/3Ca1/3MnO3
• LSDA
• random distribution of La/Ca
• Mn potential distribution 0.6eV

GWrandomness
Mn eg
Mn t2g
Mn eg
0.3eV
Mn t2g
Pickett and Singh, PRB 55, 8642 (1997)
O2p

• 0.9eV(GW minority-spin band edge)-0.3eV(Mn
  potential distribution)0.3eV
• ?
• no QP state in the minority spin component at EF
  even in the presence of disorder

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QPscGW, computational costs
LSMO, 5 atoms, upto 100eV(100bands), 20
k-points, SR11000, 4CPU
1 cycle LDA and converting data to GW
data 1hr exchange 15hr polarization
function 8hr correlation 74hr 1day for
LDAexchangepolarization (1 q4L job) 1day for
correlation (4 q4L jobs simultaneously)
About 10 cycles to be converged 20days (2.5 q4L
jobs per day)
Disk 10Gbyte
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GW Tetrahedron DOS
Lambin Vigneron, RPB 29, 3430 (1984)
An example of diamond-Si
Im(S)
A(w)
w
k(000)
ERe(S(w))
QP
Phononphotongtplariton QPplasmongtplasmonplasma
ron?
Plasmaron?
plasmon
LDA
Z0.75
LDA
qpGW
qpGW
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Future problems
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Impurity level of semiconductors
donor
acceptor
Si
Direct determination of acceptor and donor levels
GW
LDA orbital energy?quasiparticle
energy unoccupied energy level underestimated
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Antiferromagnetic Mott insulators positions of
oxigen levels

• In the AF Mott insulators, AF spin-up and -down
  bands corresponds to the upper and lower Hubbard
  bands.

LDA
GW
M?
M?
M?
?
O
O
M?
Some improvement on the energy level of ogygen?
Oxygen level is too low
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Next topic
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Complementing input files of fp-LMTO
H. Kino and H. Kotani
fpLMTO is fullpotential efficient, fast, for
bulk systems We distribute the GW programs and
would like to make it popular. The present GW
program strongly depends on the fpLMTO program.
But, it is hard to write input files of fpLMTO.
People do not use such a program.
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Interstitial region of fpLMTO
wavefunctions
potential
Interstitial region is expanded via Hunkel
functions, Parameters of Hunkel functions are
necessary. But it is not easy for beginners of
fpLMTO to give good values. What kind of values
are optimal? E.g. plane wave cutoff energy
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input files of fp-LMTO
We made scripts to complement input files of
fpLMTO
Complement each section
A minimum input file
HEADER LSMO VERS LMF-6.10 LMASA-6.10 STRUC
NBAS5 NSPEC3 NL7 ALAT7.3246
PLAT1 0 0 0 1 0 0 0
1 SYMGRP find SPEC ATOMMn Z25.0
R2.05 LMX6 qualitylow ATOMLa Z56.7
R3.3 LMX6 qualitygw1 ATOMO Z 8.0
R1.6 LMX6 MTOQs,s,0,0,0 LMX4
A0.015 SITE ATOMMn POS0.0 0.0 0.0
ATOMLa POS0.5 0.5 0.5 ATOMO POS0.5
0.0 0.0 ATOMO POS0.0 0.5 0.0
ATOMO POS0.0 0.0 0.5 HAM GMAX11
SPEC ATOM Mn Z 25.0 R 2.05 LMX 6
LMXA 4 KMXA 3 A 0.016 EH
-1.00 -1.00 -1.00 RSMH 1.37
1.37 0.91 P 4.59 4.35
3.88 4.17 5.10 IDMOD 0
0 0 1 1 ATOM La Z 56.7
R 3.3 LMX 6 LMXA 4 KMXA 3 A 0.016
EH -1.00 -1.00 -1.00 -0.20
RSMH 2.20 2.20 1.81 1.40
EH2 -0.20 -0.20 -0.20 RSMH2
2.20 2.20 1.81 P 6.57
6.21 5.85 4.13 5.13 IDMOD
0 0 0 1 1 ATOM O Z
8.0 R 1.6 LMX 6 LMX 4 A 0.015
EH -1.30 -1.00 RSMH 0.87
0.81 P 2.88 2.85 3.26
4.13 5.09 IDMOD 0 0
1 1 1
Keywords to control accuracy
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input files of fp-LMTO
We made a prototype. Many tests are necessary to
give better parameters!