In this section we investigated the electronic properties (Mulliken population charges) for the hydration adsorption on the PtSb2 (100), (110) and (111) surfaces. These properties will give insight into the chemistry bonding of the water molecule on the surfaces.
Moreover, the electron accepting and donation character of the surface and oxygen of the water molecule will be analysed.
5.2.1 PtSb
2(100) hydration surface DOS and charges
(a)
(c) (b)
(d)
respectively. The water oxygen atoms was found to adopt less negative charge, while the hydrogen atoms adopted less positive charges, suggesting charge loss and gain, respectively. Since there was no chemisorption bond between the Sb or Pt with oxygen of the water, this may imply that the oxygen has transferred charges into the H 1s-orbital from the O 2p-orbital.
Table 5.4: The calculated atomic population (Mulliken) charges of H2O molecule adsorption on PtSb2 (100) surface.
Adsorption Atom Adsorptions state
Mulliken population charges (|e|)
s p d Total Charge
Pt–OH2
Pt Before adsorption 1.00 0.85 9.08 10.97 –0.97|e–| After adsorption 0.94 0.93 9.03 10.91 –0.91|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.57 0.00 0.00 0.57 +0.43|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.86 4.96 0.00 6.82 –0.82|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.58 0.00 0.00 0.58 +0.42|e–|
Sb–OH2
Sb Before adsorption 1.84 2.95 0.00 4.79 +0.20|e–| After adsorption 1.70 2.88 0.00 4.58 +0.42|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.55 0.00 0.00 0.55 +0.45|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–|
After adsorption 1.87 5.03 0.00 6.90 –0.90|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.55 0.00 0.00 0.55 +0.45|e–| The Pt atoms were observed to have charge depletion in the s-orbital and d-orbital, with charge accumulation in the p-orbital. This suggested that the mixing of the O 2p- orbital of water with the 5d-orbital, although they did not form bonds, the 6s-orbital and 5d-orbital have transferred charges into the lower-lying regions of the Pt 5p-orbitals manifolds. This was in line with the study on Ru(H2O) on {0001} surface by Michaelides [Michaelides et al 2003]. The case of Sb atom clearly showed that both 5s-orbital and 5p- orbitals were depleted and may have distributed their charges into neighbouring surface atoms. All these findings suggested that the water molecules adsorb through Van der Waals forces on the surface.
5.2.2 PtSb
2(110) hydration surface Mulliken population charges
Table 5.5: The calculated atomic population (Mulliken) charges of H2O molecule adsorption on PtSb2 (110) surface.
Collector Atom Adsorptions state Mulliken population charges (|e|)
s p d Total Charge
Pt1–OH2
Pt1 Before adsorption 0.99 0.70 9.09 10.78 –0.78|e–| After adsorption 0.91 0.69 9.03 10.64 –0.64|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.55 0.00 0.00 0.00 +0.45|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.85 4.95 0.00 6.80 –0.80|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.58 0.00 0.00 0.58 +0.42|e–|
Pt2–OH2
Pt2 Before adsorption 0.96 0.70 9.11 10.77 –0.77|e–| After adsorption 1.91 0.72 9.08 10.71 –0.71|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.56 0.00 0.00 0.56 +0.44|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.86 4.98 0.00 6.85 –0.85|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.56 0.00 0.00 0.56 +0.44|e–|
Sb2–OH2
Sb2 Before adsorption 1.90 3.04 0.00 4.94 +0.06|e–| After adsorption 1.72 2.95 0.00 4.67 +0.33|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.54 0.00 0.00 0.54 +0.46|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.87 5.05 0.00 6.93 –0.93|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.54 0.00 0.00 0.54 +0.46|e–|
Sb3–OH2
Sb3 Before adsorption 1.85 2.95 0.00 4.80 +0.20|e|
After adsorption 1.75 2.89 0.00 4.64 +0.36|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.56 0.00 0.00 0.56 +0.44|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–|
After adsorption 1.87 5.04 0.00 6.91 –0.91|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–|
After adsorption 0.56 0.00 0.00 0.56 +0.44|e–| We found that both the Sb and Pt atoms adopt more positive charge and less negative charge, suggesting loss of charges, respectively. The water oxygen atoms was found to adopt less negative charge, while the hydrogen atoms adopted less positive charges, suggesting charge loss and gain, respectively. Since there was no chemisorption bond between the Sb or Pt with oxygen of the water, this may imply that the oxygen has transferred charges into the H 1s-orbital from the O 2p-orbital.
orbitals manifolds. This was also in line with the study on Ru(H2O) on {0001} surface by Michaelides [Machaelides et al. 2003]. The case of Sb2 and Sb3 atoms clearly showed that both 5s-orbital and 5p-orbitals are depleted and may have distributed their charges into neighbouring surface atoms. Similarly, the Pt1 showed similar behaviour as the Sb atoms, the s-p-d-orbitals have lost some charges to the neighbouring surfaces atoms. All these findings suggested that the water molecules adsorb through Van der Waals forces on the surface.
5.2.3 PtSb
2(111) hydration surface DOS and charges
The case of water adsorption on the (111) surface also showed that the water molecules did not bond on the surface. Now we analyse the atomic population charges as shown in Table 5.6, which also shows the occupancy of the s-p-d-orbitals. We found that both the Sb and Pt atoms adopt more positive charge and less negative charge, suggesting loss of charges, respectively, except for Pt1 which gained charges from the oxygen atom in all s- p-d-orbitals. The water oxygen atoms were found to adopt less negative charge, while the hydrogen atoms adopted less positive charges, suggesting charge loss and gain, respectively. Since there is no chemisorption bond between the Sb or Pt with oxygen of the water, this may imply that the oxygen has transferred charges into the H 1s-orbital from the O 2p-orbital.
The Pt2 atom was observed to have charge depletion in the s-orbital and p-orbital, with some charge accumulation in the d-orbital. This suggested that the mixing of the O 2p-orbital of water with the 5d-orbitla, although they did not form bonds, the 6s-orbital and 5p-orbital of have transferred charges into the lower-lying regions of the Pt2 5d- orbitals manifolds.
Table 5.6: The calculated atomic population (Mulliken) charges of H2O molecule adsorption on PtSb2 (111) surface.
Collector Atom Adsorptions state Mulliken population charges (|e|)
s p d Total Charge
Pt1 Before adsorption 0.96 1.00 9.06 11.02 –1.02|e–| After adsorption 0.97 1.02 9.07 11.06 –1.06|e–|
After adsorption 0.58 0.00 0.00 0.58 +0.42|e–|
Pt2–OH2
Pt2 Before adsorption 1.00 1.16 9.03 11.19 –1.19|e–| After adsorption 0.97 1.01 9.06 11.04 –1.04|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.57 0.00 0.00 0.57 +0.43|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.86 5.02 0.00 6.88 –0.88|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.57 0.00 0.00 0.57 0.43|e–|
Sb2–OH2
Sb2 Before adsorption 1.78 2.91 0.00 4.70 +0.30|e–| After adsorption 1.78 2.80 0.00 4.58 +0.42|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.55 0.00 0.00 0.55 +0.45|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.87 5.05 0.00 6.92 –0.92|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.55 0.00 0.00 0.55 +0.45|e–|
Sb3–OH2
Sb3 Before adsorption 1.78 2.91 0.00 4.69 +0.31|e–| After adsorption 1.89 2.87 0.00 4.76 +0.24|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.56 0.00 0.00 0.56 +0.44|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.87 5.04 0.00 6.91 –0.91|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.55 0.00 0.00 0.55 +0.45|e–|
Sb3(D)–OH2
Sb3(D) Before adsorption 1.62 2.93 0.00 4.55 +0.45|e–| After adsorption 1.53 2.89 0.00 4.42 +0.58|e–| H1 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.58 0.00 0.00 0.58 –0.42|e–| O Before adsorption 1.89 5.16 0.00 7.05 –1.05|e–| After adsorption 1.86 5.02 0.00 6.88 –0.88|e–| H2 Before adsorption 0.47 0.00 0.00 0.47 +0.53|e–| After adsorption 0.59 0.00 0.00 0.59 +0.41|e–| The case of Sb2 atom clearly showed that there is a charge loss only in the 5p-orbital, which may have been distributed their charges into neighbouring surface atom. The Sb3 atom have transferred charges from the 5p-orbital to the 5s-orbital. These were in line with the study on Ru(H2O) on {0001} surface by Michaelides [Michaelides et al. 2003]
All these findings suggested that the water molecules adsorb through Van der Waals forces on the surface.