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equilibrated surface has been generated, multiple snapshots that are well separated
in time are used as the input for the scattering surface. Each of these snapshots
represents a unique surface, and several such surfaces are sampled in the trajectory
calculations. Because of the nature of the QM/MM calculation, periodic boundaries
are not used, and therefore, to keep the surface density consistent over the time of
the simulation, we fix the coordinates of atoms in the outer walls and base of the
liquid as shown in Fig.
2
for O
[emim][NO
3
]. The incident atom is directed to
collide with the surface at locations that are chosen from a series of grid points
spaced ~2.5
˚
apart to ensure sampling of the various functional groups or atom
types that are present at the surface. In order to understand the angular dependence
of the scattering and not bias the incident atom to a particular angle of incidence,
several azimuthal angles are sampled and results are considered from different
incident polar angles (
y
i
) relative to the surface normal. Figure
3
provides a sche-
matic representation of this basic setup, which was utilized in our various gas-
liquid scatter experiments. In the case of our O/Ar
þ
[emim][NO
3
] studies, ten
unique surfaces, nine points on the surface grid, four azimuthal angles (0
,90
,
180
, 270
), and four incident polar angles (0
,30
,45
,60
) are considered for
þ
31.6
˚
3
QM/MM simulation box of O
Fig. 2 Side view depiction of the 32.3
[emim]
[NO
3
]. The
sticks
represent the 2,093 atoms computed with MM and the
tubes
are the 116 atoms
computed with QM. Atoms within the 5
˚
thick shaded regions
on the
sides
and
bottom
are the MM
atoms kept fixed during the simulations to keep the liquid density from changing over time
34.5
þ
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