Chemical adsorption of hydrogen atoms on graphite surfaces has attracted considerable interest due to its relevance for a broad range of areas including plasma/fusion physics, gap tuning in graphene, and hydrogen storage. We adjusted the C-H repulsive potential of the spin-polarized self-consistent-charge density-functional tight-binding (sSCC-DFTB) method to reproduce CCSD(T)-based relaxed potential energy curves for the attack of atomic hydrogen on a center carbon atom of pyrene and coronene at a tiny fraction of the computational cost. Using this cheap quantum chemical potential, we performed direct on-the-fly Born-Oppenheimer MD simulations while “shooting” H atoms with varying collision energies on a periodic graphene target equilibrated at 300 Kelvin. We compared reaction cross sections for a) elastic collisions, b) chemisorption reactions, c) penetration reactions in dependence of H/D/T kinetic energies, and found remarkable differences to previously reported classical MD simulations of the same process. Using the same potential, in simulations involving the shooting of up to 400 hydrogen atoms on the graphene sheet, we observed the self-assembly of C4H, a novel polymer with localized aromatic hexagons, in agreement with recent experimental findings.

1. Quantum Chemical Molecular Dynamics
Simulations of Graphene Hydrogenation
Stephan Irle
Department of Chemistry, Graduate School of Science
Nagoya University
第30 回 量子物理化学セミナー
Tachikawa & Kita Group
Yokohama City University, Yokohama, February 13, 2012

2. CFC: Carbon Fiber Composite
Courtesy of A. M. Ito
What do these processes have in common?
2
Introduction
Chemical reduction by
hydrogenases
Buckminsterfullerene
self-assembly
H2
2H+ + 2e-
Chemical reaction mechanisms are almost entirely unknown!
Chemical sputtering

3. 3HCN CNH
+15
+30
+45
+60
+90
+105
+120
+45
+30
+15
+60+90
+75
R
q
TS
R
P
Example: HCN  CNH isomerization
Introduction
Experimental study of complex chemical reaction
mechanism nearly impossible
Chemical reactions are theoretically studied mostly based on
•Born-Oppenheimer (BO) potential energy surfaces (PESs)
•Minimum energy reaction pathways (MERPs, result of
―intrinsic reaction coordinate‖ (IRC) calculations) Kenichi Fukui
Acc. Chem. Res. 1981
Born & Oppenheimer

4. Problems of the MERP approach:
•BO approximation and adiabatic wavefunctions may be
unsuitable, for example due to
•conical intersections/state crossings
•mixed quantum states
•high nuclear velocities (tight minima may be missed)
•entropic effects (0 Kelvin)
•quantum tunneling (hydrogen!)
4
Molecule: HCN molecule
Number of atoms N = 3
NDOF = 3N-6 = 3
•Theoretical study of chemical reactions difficult due to
dimensionality problem
Number of degrees of freedom
(NDOF):
nuclear coordinates
Brute force scan:
10 pts/DOF: 103 = 1000
energy calculations
OK!
Introduction
Hase et al. JACS 129, 9976 (2007)

5. 5
nuclear coordinates
Brute force scan:
10 pts/DOF: 10174 grid points
Molecule: C60
Number of atoms N = 60
NDOF = 3N-6 = 174
Not OK!
IRC of C60 formation?
Introduction
Self-assembly mechanism of C60
Automatized MERP Search
If we can find all TSs, then we
can find all reaction pathways
K. Ohno, S. Maeda
Chem. Phys. Lett. 384,277 (2004)
Starting from an EQ, reaction channels can be
found by following Anharmonic Downward
Distortions (ADD): Compass on the PES

6. 6
Introduction
Automatized MERP Search
Global Reaction Route Mapping (GRRM)
K. Ohno, S. Maeda, Chem. Phys. Lett. 384,277 (2004)
BUT: Number of reaction pathways presents a combinatorial explosion problem!

7. Newton’s equations of motion for the N-particle system:
Fi can be calculated as . There are several approximate methods
to solve this system of equations. Some commonly used methods are:
Verlet’s algorithm
Beeman’s algorithm
Velocity Verlet algorithm:
7
Fi = mi
˙˙ri
-¶E /¶ri
R
TS
P
     
 
i
i
iii
m
t
tttttt
2
)(
2 F
vrr ddd
   
   
i
ii
ii
m
ttt
tttt
2
FF
vv
d
dd
MD for Chemical Reactions
Introduction
Practical implementation requires discrete Dt
E can be either classical potential or Born-
Oppenheimer total electronic energy

8. Density-Functional Tight-Binding: Method using atomic parameters
from DFT (PBE, GGA-type), diatomic repulsive potentials from B3LYP
• Seifert, Eschrig (1980-86): minimum STO-
LCAO; 2-center approximation, Slater-Koster
parameter files, NO integrals!
•Porezag, Frauenheim, et al. (1995): efficient
parameterization scheme: NCC-DFTB
• Elstner et al. (1998): charge self-consistency: SCC-DFTB
• Köhler et al. (2001): spin-polarized DFTB: SDFTB
Marcus Elstner
Christof Köhler
Helmut
Eschrig
Gotthard
Seifert
Thomas
Frauenheim
8
DFTB
Alternative to DFT-based MD:
Semiclassical MD based on approximate DFT potential

9. Self-consistent-charge density-functional tight-
binding (SCC-DFTB)
M. Elstner et al., Phys. Rev. B 58 7260 (1998)
E r[ ] = ni fi
ˆH r0[ ] fi
i
valence
orbitals
å
1
  
+ ni fi
ˆH r0[ ] fi
i
core
orbitals
å
2
  
+ Exc r0[ ]
3

-
1
2
r0VH r0[ ]
R3
ò
4
  
-
- r0Vxc r0[ ]
R3
ò
5
  
+ Enucl
6
+
1
2
r1VH r1[ ]
R3
ò
7
  
+
1
2
d2
Exc
dr1
2
r0
r1
2
R3
òò
8
  
+ o 2( )
Approximate density functional theory (DFT) method!
Second order Taylor expansion of DFT energy in terms of
reference density r0 and charge fluctuation r1 (r r0 + r1) yields:
Density-functional tight-binding (DFTB) method is derived from terms 1-6
Self-consistent-charge density-functional tight-binding (SCC-DFTB)
method is derived from terms 1-8
o(3)
DFTB
9

10. DFTB and SCC-DFTB methods
 where
 ni and ei — occupation and orbital energy ot the ith Kohn-Sham
eigenstate
 Erep — distance-dependent diatomic repulsive potentials
 DqA — induced Mulliken charge on atom A
 gAB — distance-dependent charge-charge interaction functional;
gAB = gAB (UA, UB,RAB) for RAB  : Coulomb potential 1/RAB
gAA = gAA (UA, UA,RAA) for RAA  0: Hubbard UA = ½(IPA – EAA)
DFTB
10

11. DFTB method
 are tabulated for ~40 intervals as splines and have a
cutoff radius shorter than 2nd-neighbor distances; empirically fitted
 Reference density r0 is constructed from atomic densities
 Kohn-Sham eigenstates fi are expanded via LCAO-MO scheme in
Slater basis of valence pseudoatomic orbitals ci
 The DFTB energy is obtained by solving a generalized DFTB
eigenvalue problem with H0 computed by atomic and diatomic DFT
r0 = r0
A
A
atoms
å
fi = cmicm
m
AO
å
H0
C = SCe with Smn = cm cn
Hmn
0
= cm
ˆH r0
M
,r0
N
[ ] cn
DFTB
Erep
AB
(RAB )
Eigensolver: LAPACK 3.0
Divide and Conquer: DSYGVD()
Standard: DSYGV()
Intel MKL SMP-threaded parallel up to ~8 CPU cores 11

12. DFTB repulsive potential Erep
Which molecular systems to include?
DFTB
Development
of (semi-
)automatic
fitting:
•Knaup, J. et
al., JPCA, 111, 56
37, (2007)
•Gaus, M. et
al., JPCA, 113, 11
866, (2009)
•Bodrog Z. et
al., JCTC, 7, 2654,
(2011)
rep
Eab
rep
Eab
12

13. Typical number of SCC
iterations: ~10-20
Therefore: SCC-DFTB
is ~10-20 times more
expensive than DFTB
 Additional induced-charges term allows for a proper description
of polarization, charge-transfer
 Induced charge DqA on atom A is determined from Mulliken
population analysis, or equivalent
 Kohn-Sham eigenenergies are obtained from a generalized,
self-consistent SCC-DFTB eigenvalue problem
SCC-DFTB method
DFTB
13

14. Gradient for the (SCC)DFTB methods
The DFTB force formula
The SCC-DFTB force formula
computational effort: energy calculation 90%
gradient calculation 10%
Fa = - ni cmicni
¶Hmn
0
¶a
-ei
¶Smn
¶a
é
ë
ê
ù
û
ú
mn
AO
å
i
MO
å -
¶Erep
¶a
DFTB
14

15. Spin-polarized SCC-DFTB (SDFTB, sSCC-DFTB)
 for systems with different  and  spin densities, we have
 total density r = r + r
 magnetization density rS = r - r
 2nd-order expansion of DFT energy at (r0,0) yields
E r,rS
[ ]= ni fi
ˆH r0[ ] fi
i
valence
orbitals
å
1
  
+ ni fi
ˆH r0[ ] fi
i
core
orbitals
å
2
  
+ Exc r0[ ]
3

-
1
2
r0VH r0[ ]
R3
ò
4
  
-
- r0Vxc r0[ ]
R3
ò
5
  
+ Enucl
6
+
1
2
r1VH r1[ ]
R3
ò
7
  
+
1
2
d2
Exc
dr1
2
r0 ,0( )
r1
2
R3
òò
8
  
+
1
2
d2
Exc
drS
( )
2
r0 ,0( )
rS
( )
2
R3
òò
9
  
+ o 2( )
The Spin-Polarized SCC-DFTB method is derived from terms 1-9
o(3)
C. Köhler et al., Phys. Chem. Chem. Phys. 3 5109 (2001)
DFTB
15

16. where pA l — spin population of shell l on atom A
WA ll’ — spin-population interaction functional
 Spin populations pA l and induced charges DqA are obtained from
Mulliken population analysis
Spin-polarized SCC-DFTB (II)
DFTB
16

17.  Kohn-Sham energies are obtained by solving generalized, self-
consistent SDFTB eigenvalue problems
where
H-
C-
= SC-
e-
H¯
C¯
= SC¯
e¯
M,N,K: indexing specific atoms
Spin-polarized SCC-DFTB (III)
DFTB
17

18. Performance for small organic molecules
(mean absolut deviations)
• Reaction energies: ~ 5 kcal/mol
• Bond lenghts: ~ 0.014 Å
• Bond angles: ~ 2°
• Vibrational Frequencies: ~6-7 %
SCC-DFTB: general comparison with
experiment
DFTB
18

19. SCC-DFTB: Transition metals
DFTB
G. Zheng et al.J. Chem. Theor. Comput. 3 1349 (2007)
Bond lengths: ~0.1 Å
Bond angles: ~10°
Relative energies: ~20 kcal/mol
19

20. 20/25
New Confining Potentials
Wa
Conventional potential
r0
Woods-Saxon potential
k
R
r
rV 








0
)(
R0 = 2.7, k=2
)}(exp{1
)(
0
rra
W
rV


r0 = 3.0, a = 3.0, W = 3.0
Typically, electron
density contracts during
covalent bond formation.
In standard ab initio
methods, this is easily
handled by n-z basis
sets.
DFTB uses minimal
valence basis set: the
confining potential is
adopted to mimic
contraction
• •+
• •
1s
σ1s
H H
H2
e.g
.
Δρ = ρ – Σa ρa
H2 difference density
1s
DFTB Parameterization
Prof. Henryk
Witek, National Chiao
Tung University, Taiwan
20

21. Each particle has
randomly generated
parameter sets (r0, a, W)
within some region
Generating one-center
quantities (atomic
orbitals, densities, etc.)
―onecent‖
Computing two-center
overlap and Hamiltonian
integrals for wide range
of interatomic distances
―twocent‖
―DFTB+‖
Calculating DFTB band
structure
Update the parameter
sets of each particle
Memorizing the best fitness
value and parameter sets
*a [2, 4]
W [0.1, 5]
r0 [1, 10]
Evaluating ―fitness value‖
(Difference DFTB – DFT band
structure using specified fitness
points) ―VASP‖
“Particle Swarm Optimization”
DFTB Parameterization
21

22. Chou, Nishimura, Irle, Witek, In preparation
Error in DH for linear
alkanes CnH2n+2
Automatization of Erep
Parameterization
22
DFTB ParameterizationElectronic parameters now available for Z=1-83!
Yoshifumi Nishimura, D2
Future: GA-based Erep parameterization
Or on-the-fly parameterization 22

23. DFTB ParameterizationTransferability of optimum parameter sets
for different structures
Artificial crystal structures can be reproduced well
e.g. : Si, parameters were optimized with bcc only
W (orb) 3.33938
a (orb) 4.52314
r (orb) 4.22512
W (dens) 1.68162
a (dens) 2.55174
r (dens) 9.96376
εs -0.39735
εp -0.14998
εd 0.21210
3s23p23d0
bcc 3.081
fcc 3.868
scl 2.532
diamond 5.431
Parameter sets:
Lattice constants:bcc fcc
scl diamond
Expt
.

24. DFTB ParameterizationTransferability of optimum parameter sets
for different structures C, diamond + graphite, 2s22p2
DFT
DFTB
Orbital energy:
2s = -0.50533
2p = -0.19423
diamond graphite
Band gap:
5.35 eV (DFT)
7.23 eV (DFTB)
7.3 eV (expt.)

25. Rocksalt (space group No. 225)
•NaCl
•MgO
•MoC
•AgCl
…
•CsCl
•FeAl
…
B2 (space group No. 221)
Zincblende (space group No. 216)
•SiC
•CuCl
•ZnS
•GaAs
…
Others
•Wurtzite (BeO, AlO, ZnO, GaN, …)
•Hexagonal (BN, WC)
•Rhombohedral (ABCABC stacking
sequence, BN)
No further optimization of parameters
more than 100 pairs tested
DFTB ParameterizationBinary compounds
25

26. •d7s1 is used in
POTCAR (DFT)
Further improvement can be performed for specific purpose but
this preliminary sets will work as good starting points
NaCl (rocksalt) FeAl (b2)
CsF (rocksalt) BN (wurtzite)
•matsci-0-2 for
previous work
DFTB ParameterizationBinary compounds: Selected examples
26

27. Experimental
Chemisorption of
atomic hydrogen •Fully saturated
graphene with
sp3 hybridization
(diamond-like)
•Band gap of
~3eV
Band insulator!
―Graphane‖, J. O. Sofo et
al., Phys. Rev. B, 77 153401
(2007).
DFT calculations for partially
hydrogenated graphene show:
1. Band gap at K-opening
2. Dispersionless hydrogen
acceptor level at EF
3. Spin splitting
E. J. Duplock et al., Phys. Rev
Lett., 92, 225502 (2004). 27

28. Hydrogen plasma - wall interactions (PWI) in nuclear
fusion reactors
LHD (Large Herical Device)
A. Sagara et al, (LHD Experimental Group, National Institute for Fusion Science, Gifu),
J. Nucl. Mater. 1, 313 (2003)
Divertor plate
(Graphite)
Experimental
28

29. Hydrogen-wall interaction
⇒H2, CHX, C2HX formation
Observable on graphite divertor
and in plasma-beam experiments
CyHX formation
mechanism unknown
Atomic-scale simulation of CyHX formation
CFC: Carbon Fiber Composite
Experimental
Hydrogen plasma - wall interactions (PWI) in nuclear
fusion reactors
29

30. Reactive Empirical Bond Order (REBO) force field MD
simulations of atomic hydrogen reactions with graphite
(0001)
H incident energy: 5 eV
Injection rate: 1 H/0.1 ps
―Graphite peeling‖
A. Ito, Y. Wang, SI, K. Morokuma, H.
Nakamura, J. Nuclear Mater. 300, 157
(2009).
REBO vs DFTB
30

31. -Two-body potential
-No effects of pconjugation or aromaticity included
-Typically too high sp3 carbon fraction (Marks et al. Phys.
Rev. B 65, 075411 (2002))
-Typically too low fraction of sp carbons (SI, G.
Zheng, Z. Wang, K. Morokuma, J. Phys. Chem. B
110, 14531 (2006))
How trustworthy is REBO in this case?
Parameterize cheap QM method for MD!
Drawbacks of REBO
REBO vs DFTB
31

32. Fitting of Density-Functional Tight-Binding:
Adjusting Erep for H-graphene chemisorption
Extended Hückel type method using atomic parameters from DFT
(PBE, GGA-type), diatomic repulsive potentials from B3LYP
• Seifert, Eschrig (1980-86): STO-LCAO; 2-center approximation
• Porezag et al. (1995): efficient parameterization scheme: NCC-DFTB
• Elstner et al. (1998): charge self-consistency: SCC-DFTB
• Köhler et al. (2001): spin-polarized DFTB: SDFTB
Adjust Erep for C-H!
REBO vs DFTB
Self-consistent charge-charge interactions
Self-consistent spin-spin interactions
Zeroth-order Hamiltonian: no e-e interactions
32

33. Pyrene
C16H10

X//B3LYP/pVDZ relaxed energy profiles for PAH models
Barrier:
+6.9 kcal/mol (B3LYP)
+9.2 kcal/mol (G2MS)
Well depth:
-9.1 kcal/mol (B3LYP)
-9.0 kcal/mol (G2MS)
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.5 1.5 2.5 3.5
Bindingenergies(ineV)
C-H distance (in Angstrom)
UB3LYP
ROMP2/DZ//UB3LYP
ROCCSD//UB3LYP
ROCCSD(T)//UB3LYP
G2MS
REBO vs DFTB
Coronene
C24H12
 Barrier:
+6.8 kcal/mol (B3LYP)
+10.1 kcal/mol (G2MS)
Well depth:
-10.2 kcal/mol (B3LYP)
-10.1 kcal/mol (G2MS)
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.5 1.5 2.5 3.5
Bindingenergy(ineV)
C-H distance (in Angstrom)
UB3LYP
ROMP2/DZ//UB3LYP
ROMP2/TZ//UB3LYP
RCCSD//UB3LYP
RCCSD(T)//UB3LYP
G2MS
~1.5 CPU years
33

34. -40.00
-35.00
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
5.00
10.00
0 1 2 3 4
energy(inkcal/mol)
C-H distance (in A)
Erep
Erep-wish
Erep-sdftb
-40.00
-35.00
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
5.00
10.00
0 1 2 3 4
energy(inkcal/mol)
C-H distance (in A)
Erep
Well depth nearly same, but barrier height should be enhanced by ~5 kcal/mol
Blue: DE(UB3LYP/pVDZ)//B3LYP/pVDZ
Red curve: original DE(SDFTB)//B3LYP/pVDZ

REBO vs DFTB
X//B3LYP/pVDZ relaxed energy profiles for PAH models
34

35. -2.0
-1.5
-1.0
-0.5
0.0
0.5
0.5 1.5 2.5 3.5
RelativeEnergy[eV]
C-H distance [Å]
B3LYP
RCCSD(T)
G2MS
SCCDFTB
SDFTB-original
SDFTB*
REBO vs DFTB
X//B3LYP/pVDZ relaxed energy profiles for PAH models

SDFTB* now reproduces G2MS curve exactly at tiny amount of computer time
35

36. 36

37. 3 qualitatively distinct types of reaction outcomes:
Reflection: EI < 1eV
Adsorption: 1eV < EI < 7eV
Reflection: 7eV < EI < 30eV
Penetration: EI > 30eV
REBO Simulations by Ito et al.
Contrib. Plasma Phys. 48, 265 (2008)
REBO vs DFTB
37

38. REBO vs DFTB
0.0
0.2
0.4
0.6
0.8
1.0
0.1 10
Ratio
Incident Energy （in eV)
SDFTB*
Absorption (forward)
Absorption (backward)
Reflection
Penetration
REBO
REBO: Barrier 0.5 eV, height
OK, but too thin
Well -4.8 eV, much too low
REBO
38

39. REBO vs DFTB
0.0
0.2
0.4
0.6
0.8
1.0
0.1 10
Ratio
Incident Energy （in eV)
SDFTB*
Absorption (forward)
Absorption (backward)
Reflection
Penetration
REBO
0.0
0.2
0.4
0.6
0.8
1.0
0.1 10
Ratio
Incident Energy (in eV)
Deuterium Absorption (forward)
Absorption (backward)
Reflection
Penetration
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10 100
Ratio
Incident Energy(in eV)
Tritium
Absorption (forward)
Absorption (backward)
Reflection
Penetration
39

40. 2D potential of hydrogen atom in the hexagon plane
REBO SDFTB*
REBO vs DFTB
40

41. -2.5
-2
-1.5
-1
-0.5
0
0.5
1
1 1.1 1.3 1.5 1.7 2 2.5 3
Relativeenergy(ineV)
C-H distance (in Angstrom)
DFTB+
1H-M=2-Te=0
2H-M=1-Te=0
2H-M=3-Te=0-initial-spin
2H-M=1-Te=0-initial spin
2 Hydrogen atoms on graphene: Singlet or triplet?
Top view
Side view
1H: SDFTB* Doublet
2H: SCC-DFTB closed-shell
singlet
2H: SDFTB* triplet
2H: SDFTB* open-shell singlet
Evidence for long-distance spin
correlation via pconjugation!
Cannot be captured classically!
REBO vs DFTB
41

42. 42
C4H Polymer
Experiment: chemical environment of hydrogenated graphene
Quasi-free-
standing
grapheneHydrogenated
quasi-free
standing
graphene
D. Haberer et al. Nano Lett. 10, 3360 (2010) 42

43. H coverage from High-resolution XPS
C4H Polymer
D. Haberer et al. Adv. Mater. 23, 4497 (2011) 43

44. H coverage as function of time
Why does it stop at 25%??
C4H Polymer
D. Haberer et al. Adv. Mater. 23, 4497 (2011) 44

45. Simulation details
• Ten trajectories for 1 eV and 0.4 eV incident energies
• NVT (Tn=300 K, Nose-Hoover chain thermostat), 4*4 unit
cell (32 carbon atoms)
• H were ―shot‖ at perpendicular angular from 3 Å distance,
random x and y coordinates, random spin
• Totally 100/400 H were ―shot‖
• 1H/0.5 ps, Dt = 0.2 fs (ensure energy conservation in NVE)
• New G2MS-derived C-H Erep
• SDFTB with Te=300 K
C4H Polymer
45

46. 46
1 2 3 4 5
6 7 8 9 10
Boukhvalov. et.al JPCC 113,14176 (2009)
C4H Polymer
All H-frustrated
Flores
et.al, Nanotechnology, 20
Incident energy: 1 eV
46

47. Average H Coverage Reaction processes
0
0.1
0.2
0.3
0.4
0 10 20 30 40 50
RatioofH/C
Time (ps)
0
20
40
60
80
100
0 10 20 30 40 50
NumberofH
Time (ps)
reflection
adsorption
h2 formation
C4H PolymerIncident energy: 1 eV
47

48. 2 and 3 show perfect ―para-structure‖,
others are mixed para/H-frustrated
C4H PolymerIncident energy: 0.4 eV
Much less H-frustration
48

49. 49
0
100
200
300
400
0 50 100 150 200
NumberofH
Time (ps)
reflection
adsorption
h2 formation
Reaction processes
(average over 10 trajectories)
C4H PolymerIncident energy: 0.4 eV
0
5
10
15
0 50 100 150 200
NumberofH
12
4
8
D. Haberer et al. Adv. Mater. 23, 4497 (2011)
49

50. Why 25%? C4H possesses an “all-para” structure with
aromatic superlattice!
D. Haberer et al. Adv. Mater. 43, 4497
(2011)
C4H Polymer
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1 1.5 2 2.5 3
Relativeenergy(eV)
C-H distance (Angstrom)
C4H+H
C+H
• C4H has higher hydrogenation
barrier of about 0.63 eV, higher
than incident energy of 0.4 eV.
• Potential energy profile of C4H+H
is shallower than graphene+H.
graphene+H
50

51. 51
C4H Polymer
How does the surface really look like?

52. • Maximum H coverage depends on the incident energy,
higher incident energy gives higher coverage
• Higher incident energy (1 eV) yields H-frustrated
structure, while lower incident energy (0.4 eV) can lead to
self-assembled para-hydrogenated structure  similarity
to crystallization
• Stability of C4H para-hydrogenated structure caused by:
1. local aromaticity
2. High barrier for attack on aromatic hexagons
3. Low reverse barriers for hydrogen loss from aromatic hexagons
C4H Polymer
52

53. • Recently, Grüneis found substantial isotope effects
(unpublished):
- Deuteration has higher adsorption maximum than H
- Deuterium can completely replace H on graphene, but
not vice versa
D/H Isotope Effect
53

54. D/H Isotope Effect
54
Averaged coverage Reflecion-Adsorption-H2
H
R:A:H2=479.6:14.0:6.4
D
R:A:H2=479.7:14.7:5.6
D has more adsorption (14.7 VS. 14.0) and less D2/H2
leaving (5.6 VS. 6.4) than H---- larger coverage
R
A H2
Incident energy: 0.4 eV

55. Acknowledgements
The Group:
Dr. Ying Wang
Dr. Hu-Jun Qian
Dr. Matt Addicoat (JSPS)
Dr. Cristopher Camacho
Mr. Yoshifumi Nishimura (D1)
Mr. Yoshio Nishimoto (M2)
Undergraduates
Ms. Yae Imai
(Administrative Assistant)
Collaborators: Keiji Morokuma (Kyoto U, Emory U)
CREST “Multiscale Physics” (2006-2011)
CREST “Soft pmaterials: (2011-2015)
SRPR tenure track program (2006-2011)
JSPS
KAKENHI
Funding:
July 8, 2011