The initial structure used to start the MD simulation: Five water molecules randomly located on a rutile (110) surface cell of a five layer periodic slab; only the symmetry independent layers of the model system, where the molecules are present on both sides of the slab, are shown. The gray, red, and green spheres represent the titanium, oxygen, and hydrogen atoms, respectively.
Temperature vs time during the MD simulation after .
Side and top view of the adsorbate structure with lowest free energy in our MD simulation. The nonequivalent oxygen atoms considered for the simulation of the XPS spectrum are labeled by numbers also reported in Fig. 6. The red, dark red, and light red spheres represent the bulk oxygen, the surface bridging oxygen, and the oxygen in waters, respectively. The hydrogen bonds are also shown by blue dashed lines.
Inter atomic distances O–H (a) and Ti–O (b) vs time during the last of the MD simulation. The labeling of oxygen atoms corresponds to the numbering reported in Fig. 3. The dotted line in (a) shows the distance between H atoms left on the dissociated water molecule [O(5)H] and the bridging oxygen O(1) that forms a second OH. The solid black line in (a) shows the distance between the oxygen atom O(5) of dissociated water and the hydrogen atom that goes away toward the neighbor bridging oxygen O(1). The solid grey line in (a) shows the distance between the bridging oxygen O(1) and the adsorbed hydrogen atom deriving from the water dissociation. The first three lines, from top to bottom, in (b) show the distance between the oxygen atom of different water molecules (see Fig. 3 for numbering) and their underling fivefold-coordinated titanium atoms. The last line in (b) shows the distance between the oxygen atom in the dissociated water [O(5)H] and its underling titanium atom.
Calculated photoemission spectra of adsorbate for 12 configurations taken out from the last of the MD simulation with equal time step. The main peak corresponds to the lowest binding energy. The continuous profile was obtained by a Lorentzian convolution .
Calculated photoemission spectrum of adsorbate compared to the experimental spectrum (Ref. 7) in the inset. The theoretical spectrum was shifted to put the binding energy of the bulk peak A at the experimental value of . The bar diagram is obtained by the computed binding energies and the relative intensities corresponding to the numerical weight of each nonequivalent oxygen atom in our model. The continuous line is a Lorentzian convolution . The dashed lines are peak indicators. The numbers in parentheses correspond to the numbering of oxygen atoms in Fig. 3.
Adsorption energy (in eV) for molecular and dissociative adsorption and geometry parameters (in Å) (distance between the oxygen atom of the adsorbed water molecule and the closest Ti atom) and (shorter distance between a hydrogen atom of the water molecule and a bridging oxygen on the surface) in the three test models. is defined as the difference between dissociative and molecular adsorption energies.
Assignment of the main features in the XPS spectrum of the system.
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