Scanned-energy mode photoelectron diffraction (PhD) and ab initio density functional theory calculations have been employed to investigate the adsorption geometry of benzoate ([C6H5COO](-)) on rutile-TiO2(110)(1 X 1). PhD data indicate that the benzoate moiety binds to the surface through both of its oxygen atoms to two adjacent fivefold surface titanium atoms in an essentially upright geometry. Moreover, its phenyl (C6H5-) and carboxylate ([-COO](-)) groups are determined to be coplanar, being aligned along the [001] azimuth. This experimental result is consistent with the benzoate geometry emerging from DFT calculations conducted for laterally rather well separated adsorbates. At shorter interadsorbate distances, the theoretical modeling predicts a more tilted and twisted adsorption geometry, where the phenyl and carboxylate groups are no longer coplanar; i.e., interadsorbate interactions influence the configuration of adsorbed benzoate.

Hybrid exchange density functional theory is used to model defects on the beta-AlF(3) (100) surface. The stability of the surface with respect to the diffusion of surface F ions is investigated. It is shown that under typical reaction conditions (600 K) the surface is not kinetically hindered from reaching thermodynamic equilibrium. A reaction mechanism for the catalysis of 2CCl(2)F(2)--> CClF(3) + CCl(3)F is proposed. The mechanism and corresponding reaction barriers are calculated using a double-ended transition state search method. It is predicted that the processes that determine the overall reaction rate occur at defect sites.

Low-energy electron-diffraction and surface x-ray diffraction data acquired from TiO2(110)(1X1) are re-analyzed to confirm the integrity of the previously reported optimized geometries. This work is performed in response to ab initio density-functional theory calculations that suggest that the atomic displacements determined from low-energy electron-diffraction measurements may be compromised by the limited number of optimized atom positions. Performing structural optimizations as a function of depth into the selvedge, this present study validates the previous experimental structure determinations.

An understanding of the phase stability of AlF3 surfaces as a function of their environment is an important prerequisite in the development of, and an ability to control, their catalytic properties. In this study, all electron hybrid-exchange density functional theory is used to calculate the structure and corresponding energies of several α-AlF3 surfaces. It is shown that the surfaces expose under-coordinated Al ions that are potential Lewis acid sites. The binding energy of NH3 to these sites is calculated and used to quantify their relative acidities. The Lewis acid sites are significantly weaker than the strongest sites predicted to occur on β-AlF3 surfaces. The equilibrium morphology of α-AlF3 crystallites is predicted from the construction of an approximate Wulff plot. The stabilities of two representative terminations of α-AlF3, as a function of HF and H2O chemical potentials are computed using ab initio thermodynamics. The geometries of their stable surfaces are found to be strongly dependent on the environmental conditions.

An understanding of the phase stability of AlF3 surfaces as a function of their environment is an important prerequisite in the development of, and an ability to control, their catalytic properties. In this study, all electron hybrid-exchange density functional theory is used to calculate the structure and corresponding energies of several alpha-AlF3 surfaces. It is shown that the surfaces expose under-coordinated Al ions that are potential Lewis acid sites. The binding energy of NH3 to these sites is calculated and used to quantify their relative acidities. The Lewis acid sites are significantly weaker than the strongest sites predicted to occur on beta-AlF3 surfaces. The equilibrium morphology of alpha-AlF3 crystallites is predicted from the construction of an approximate Wulff plot. The stabilities of two representative terminations of alpha-AlF3, as a function of HF and H2O chemical potentials are computed using ab initio thermodynamics. The geometries of their stable surfaces are found to be strongly dependent on the environmental conditions.

The recently discovered high surface area AlF3 catalyst is characterised with respect to surface composition and structure using calculations based on density functional theory. Under typical reaction conditions the surfaces are found to expose five fold coordinated Al reaction centres and to preferentially adsorb water. The acidic centres are probed using NH3 adsorption which binds strongly indicating strong Lewis acidity. The predicted temperature probed desorption spectrum has features from competing surfaces and features due to strong intermolecular interactions, which are used to interpret the observed spectrum.

The structure of an ordered (2 x 1) overlayer of [HCOO](-) on rutile TiO(2)(110)(1 x 1) has been elucidated using quantitative low energy electron diffraction. Both the location of adsorbate atoms, and substrate relaxation are determined. In agreement with previous work, it is concluded that the formate moiety binds to the surface through both of its oxygens to two adjacent 5-fold surface titanium atoms, so that its molecular plane is aligned with the 10011 azimuth, i.e., it lies parallel to the bridging oxygen rows. The local adsorption geometry is in excellent quantitative agreement with that derived in a recent photoelectron diffraction study (Sayago, D. I., et al. J. Phys. Chem. B 2004, 108, 14316).

The current study employs hybrid-exchange density functional theory to investigate the adsorption of HF and HCl to under-coordinated Al ions on the beta-AlF3 ( 100) surface. It is shown that the geometries of the adsorbates are strongly dependent on coverage. Furthermore, the adsorption of HCl leads to a number of distinct structures that have very similar energies. It is proposed that this result may explain the high catalytic activity of aluminium fluoride and aluminium chloro-fluoride surfaces towards chlorine-fluorine exchange reactions. The stretching and bending frequencies of the H-F and H-Cl bonds at half and full monolayer coverage are also calculated and the vibrational spectrum is found to be strongly dependent on the adsorption site and the coverage. The vibrational frequency shifts provide, therefore, a mechanism for experimentally characterising these surfaces.

The current study employs hybrid-exchange density functional theory to show that the Lewis base, NH(3), binds to the beta-AlF(3) (100) surface with a binding energy (BE) of up to -1.96 eV per molecule. This is characteristic of a strong Lewis acid. The binding of NH(3) to the surface is predominately due to electrostatic interactions. There is only a small charge transfer from the NH(3) molecule to the surface. The BE as a function of coverage is computed and used to develop a lattice Monte Carlo model which is used to predict the temperature programed desorption (TPD) spectrum. Comparison with experimental TPD studies of NH(3) from beta-AlF(3) strongly suggests that these structural models and binding mechanisms are good approximations to those that occur on real AlF(3) surfaces.

The current study employs state of the art hybrid-exchange density functional theory (DFT) to investigate the Lewis acidic sites on the β-AlF3 (100) surface. It is shown that the strong Lewis base, NH3, binds to the surface with a binding energy of up to 1.9 eV. This demonstrates that the material is strongly Lewis acidic. We also consider the binding of the weak Lewis base CO to the surface. We calculate the shift in its stretch frequency compared to the gas phase molecule. Shifts are compared to experimental data and are shown to be typical of strong Lewis acidity.

First principles simulations of steps on the β-AlF3 (100) surface between two, previously identified, low-energy terminations have been performed. The optimization of these structures leads to the formation of microfacets having the (010) orientation. The microfaceted surface is found to have a lower surface energy than either of the low-energy terminations used to construct the model stepped system. This suggests that the (100) surface is not, thermodynamically, the most stable termination of β-AlF3. We have therefore also investigated the structure and stability of the (010) and (001) surfaces and find that both of these surfaces are lower in energy than the (100) surfaces. The surface energies of these planes are used to construct an approximate Wulff plot and thus predict the equilibrium crystal morphology.

The methodology for the calculation of the phase stability of different surfaces in contact with a multi component environment of gases is presented. The evaluation of the surface free energy of a system is discussed in detail including the use of thermodynamic data tables.

Thermodynamic calculations based on hybrid-exchange density functional theory are used to predict the surface structure and stability of α-AlF3 (011¯2) in the presence of gaseous HF and H2O environments. The clean stoichiometric α-AlF3 (011¯2) is predicted to be Lewis acidic. However, under most reaction conditions this surface is unstable with respect to the adsorption of hydroxyl ions. This is consistent with experimental observations. It is predicted that the surface containing no hydroxyl ions could only be realised at high temperatures and under unrealistically dry conditions.

Grid computing is becoming an increasingly important way fo r c mputational scientists to access computer resources. However, there is currently no consensus on the opt imum middleware for providing access to these resources, or even a uniform way for users to interact with a particular m iddleware solution. As part of our work on the NWGRID project, and in our development of our CCP1 GUI software , w have had cause to use two of these solutions (Globus and NorduGrid ARC), together with various client-s ide tools that are under development to support them. This paper describes our experiences to date with these diff erent solutions, and work that has been carried out using some of them.

Solid aluminium fluorides have great potential for use in a range of reactions that are catalysed by strong Lewis acids. However, very little is known about the detailed atomic scale structure of their surfaces. We present new results for the surface structure of beta-AlF3 based on first principles simulation and compare these with our earlier work on alpha-AlF3. On the basis of these simulations we can explain the observed reactivity of the aluminium fluoride materials. We can also use these results to postulate a mechanism for the observed high reactivity shown by amorphous, 'high-surface area' AlF3.

Aluminum chloride is used extensively as Lewis acid catalyst in a variety of industrial processes, including Friedel-Crafts and Cl/F exchange reactions. There is a common misconception that pure AlCl3 is itself a Lewis acid. In the current study, we use experimental and computational methods to investigate the surface structure and catalytic properties of solid AlCl3. The catalytic activity of AlCl3 for two halide isomerization reactions is studied and compared with different AlF3 phases. It is shown that pure solid AlCl3 does not catalyze these reactions. The (001) surface of crystalline AlCl(3) is the natural cleavage plane and its structure is predicted via first principles calculations. The chlorine ions in the outermost layer of the material mask the Al3+ ions from the external gas phase. Hence, the experimentally found catalytic properties of pure solid AlCl3 are supported by the predicted surface structure of AlCl3.