Transcript Yoshiyuki Miyamoto

Yoshiyuki Miyamoto’s talk
Please standby.
Yoshiyuki Miyamoto’s talk
Please standby.
“Computational Challenges and Tools for Nanotubes"
Sunday 26 June 2005, 13:00 -??:??
Studenternas Hus, Götabergsgatan 17, S-41134 Göteborg, Sweden
Simulation of Excited State Dynamics in Nanotubes
with Use of the Earth Simulator
Yoshiyuki Miyamoto
Fundamental and Environmental Res. Labs.
Acknowledgements:
Osamu Sugino, ISSP, U-Tokyo
Noboru Jinbo (RIST→TOSHIBA)
Hisashi Nakamura (RIST)
Savas Berber (Michigan State Univ.→Tsukuba Univ.)
Mina Yoon (Michigan State Univ.→ORNL)
Angel Rubio (Univ. Páis Vasco, Spain)
David Tománek (Michigan State Univ.)
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How to simulate excited state dynamics?
(An approximated way)
Potential
|e>
|g>
Constraint DFT
Reaction coordinate
Time-dependent method can follow  n (t  dt )  exp( iH ) n (t )
with no need of occupation assignment at every time-step.
Sugino & Miyamoto PRB 59, 2579 (1999) ; ibid, B 66, 89901(E) (2002).
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Parallel computing
with respect to each
wave function
CPU 1:
Ψ1(t+Δt)=exp{-i/ħΔtHKS(t)} Ψ1(t)
HKS (t+Δt)
|Ψ1(t+Δt)|2
HKS (t+Δt) CPU 2:
Ψ2(t+Δt)=exp{-i/ħΔtHKS(t)} Ψ2(t)
CPU 0:
|Ψ2(t+Δt)|2
ρ(t+Δt)=Σ|Ψi(t+Δt)|2
HKS (t+Δt)=HKS{ρ(t+Δt)}
MPI_Reduce & MPI_Bcast
|Ψn(t+Δt)|2
HKS (t+Δt)
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CPU n:
Ψn(t+Δt)=exp{-i/ħΔtHKS(t)} Ψn(t)
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Textbook for ‘TDDFT’ from Springer will soon appear
(I hope)!
Edited by E. U. K Gross, et al.
- Contents Principle (Runge & Gross)
Perturbation theory
Current density functional
Non-adiabatic xc potential
Real-time for finite systems (Rubio, et al.)
Real-time for extended systems (Sugino & Miyamoto)
etc..
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1. Elimination of impurities from nanotubes by
optical surgery.
2. Hot-carrier relaxation in nanotubes
3. Some notes for fluorescence from (n,0) tubes
4. Summary
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Electronic excitation as a tool of cleaning!
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(3,3) defected tube with O
(Oxidized)-(O-free)
A.Potential
Kuznetsova, Profile
et al., J. Am.
Chem. Soc. 123,
10699 (2001)
NEXAFS
O
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CNT
C.B.
O-related
electronic
levels
O 2p
O
CNT
V.B.
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O 2s
Auger decay after O 1s to 2p excitation (~520 eV)
Atomic scale surgery of O-extraction from NT.
O 2p
H2
A gaping wound
C.B.
CNT
V.B.
30 fs
Nanotube can heal its wound!
O 2s
Combination of H2 introduction
and electronic excitation:
60 fs
126 fs
O 1s
Post fabrication processing
[More details, Miyamoto, et al., PRB70, 233408 (2004).]
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Electronic excitation and subsequent decay
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Nanotube devices: FET, non-linear optical devices
Switching Frequency – lifetime of excited carriers
Hertel and Moos, PRL 84, 5002 (2000)
e-e comes before e-ph
Ichida, et al., Physica B 323, 237 (2002)
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Hot carrier decay in (3,3) nanotube under assumed
lattice temperature
electron
hole
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/96 atom
Energy transfer between electrons and ions
electron-electron
is dominant
electron-phonon
is dominant
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Some notes for fluorescence from (n,0) tubes
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Excitation
Identification of semiconductor nanotubes by fluorescence
Miyauchi et al., CPL 387, 198, (2004)
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Question!
Can we see light-emission from thinner (n,0) tubes?
(LDA:2.98eV)
(LDA:2.94eV)
Electronic structure of (7,0): LDA
HO-LU pair is optically inactive!
Many possible decay paths into
optically forbidden e-h pairs
π-band T.B.
model cannot
reproduce this
(LDA:0.94eV)
band.
Time-constant of the
possible decays should be
checked by TDDFT-MD
simulations!
(LDA:2.33eV)
(LDA:
2.31eV)
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1. TDDFT-MD simulation has become able beyond 500 fs.
2. We start from constraint DFT with Hellmann-Feynman force
(Ehrenfest approach)
3. Application to nanotubes
• photo-induced defect dynamics
• decay dynamics of hot carriers
• examination of luminescence from (n,0) tubes (future works)
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How to simulate excited state dynamics?
t = 0: Promote the electronic occupations to mimic the
excited states. Then perform the static SCF calculation.
Potential
t > 0: Solve ψn(t+Δt)=exp{- i ΔtH(t)} ψn(t).
|e>
Hellmann-Feynman theorem
works
Is the matrix of HKohn-Sham Yes
Do MD.
diagonal?
|g>
1.
No need ofmonitoring
level assignment
for a hole and
an excited
electron
2. Automatic
of the nonradiative
decay
(lifetime,
except
at coordinate
thewithout
beginning.
decay path)
experiences.
Reaction
No
Observation of the nonradiative decay!
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lifetime,
decay path
Potential
Excited
state
dynamics
Ground
state
theory!
What code is used? Solving
thethe
time-dependent
problem
Solving
eigenvalue problem
d n
H n H

i

|e>
nnn
dt
TM
Many software packages (VASP,
CASTEP, GAUSSIAN, etc.)
|g>
First-Principles Simulation tool for
Electron-Ion Dynamics
Reaction coordinate
Sugino & Miyamoto PRB 59, 2579 (1999) ; ibid, B 66, 89901(E) (2002).
Computational conditions (on the basis of standard
band structure calculation
1. TDLDA (with adiabatic xc potential)
2. Troullier-Martins type separable pseudopotentials
3. Plane wave Cutoff energy: 40 Ry, 60 Ry
4. Time step: 0.08 a.u. (=0.0019 fs), 0.05 a.u.(=0.0012 fs)
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