Chemistry Reference
In-Depth Information
Fig. 10.3 a-b Sequential STM images and schematic illustration of the assembly process of an
H
2
O-(OH)
3
complex from (OH)
2
and H
2
O-OH (38 9 38 Å
2
, V
s
= 30 mV and I
t
= 0.5 nA). The
white grid lines indicate the lattice of the Cu(110) surface and the dots represent the short-bridge
sites occupied by oxygen atoms. The H
2
O-OH complex is moved along the [110] direction
(dashed arrow) with the STM, and reacted with the (OH)
2
to yield an H
2
O-(OH)
3
complex
bounded at the short-bridge site. It is noted that the water molecule and its
neighboring hydroxyl are strongly interacted via H bond and they are slightly
deviated from the exact short-bridge position. The corresponding simulated STM
image
2
(Fig.
10.6
b) is characterized by a ''tadpole''-shaped protrusion with the
head and tail appeared over the water molecule and hydroxyl groups, respectively,
being in good agreement with the experimental appearance.
(Footnote 1 continued)
used to expand wave functions and augmentation charge, respectively. The Cu(110) surface was
modeled by a five-layer slab with a 4 9 3 periodicity, and a vacuum region of 12.89 Å was
inserted between slabs. The slab was constructed using the lattice constant optimized by PBE-
GGA (a
0
= 3.64 Å). An H
2
O-(OH)
2
complex was put on one side of the slab and spurious
electrostatic interaction was eliminated by the effective screening medium method [I. Hamada
et al. Phys. Rev. B 80, 165411 (2009).]. Adsorbate and topmost two Cu layers were allowed to
relax until the forces were less than 0.05 eV/Å, and remaining Cu atoms are fixed at their
respective bulk positions. Brillouine zone sampling was done using a 4 9 2 Monkhorst-Pack k-
point set [H.J. Monkhorst and J.D. Pack, Phys. Rev. B 13, 5188 (1976).] and Fermi-surface was
treated by the first-order Methfessel-Paxton scheme [A. Methfessel and A.T. Paxton, Phys. Rev.
B 40, 3616 (1989).] with the smearing width of 0.05 eV.
2
For the STM simulations, a dense 16 9 8 k-point set was used. Adsorbate and topmost two Cu
layers were allowed to relax, and remaining Cu atoms are fixed at their respective positions. STM
simulations were conducted within the Tersoff-Hamman theory [J. Tersoff and D.R. Hamann,
Phys. Rev. Lett. 20, 1998 (1983).]. In the STM simulations, the sample bias voltage was set to
25 mV, and images were obtained at the constant height of 7 Å from the topmost Cu plane.
