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Plane-wave density functional theory (DFT-PW) calculations were performed on bulk SnO(sub 2) (cassiterite) and (100), (110), (001), (101) surfaces with and without H(sub 2)O present to assess the atomic structure of the oxide-water interface. The experimental crystal structure and elastic constants of SnO(sub 2) are reproduced reasonably well with the force field and surface atom relaxations while the structures of adsorbed H(sub 2)O molecules agree well between the ab initio and force field predictions.

A force field for interactions of water molecules with the (110) surface of rutile (alpha-TiO2) is generalized for atomistically detailed molecular dynamics simulations. The positions of water molecules at the interface are examined.

Periodic (CASTEP and Dmol(super 3)) and cluster (Gaussian 98 and DMol(super 3)) ab initio calculations are carried out to develop force field parameters for the system Ti-O-H to model TiO2-H2O interfaces. The H-bond length between an adsorbed water molecule and the neighboring bridging oxygen is approximately 1.8 angstroms.

The periodic density functional theory (DFT) based on plane waves (PW) and Hartree-Fock (HF) based on the linear combination of atomic orbitals (LCAO) calculations, using the slabs separated by vacuum gaps, were carried out to model the H2O-TiO2 (rutile) (110) interface. The role of H-bond formation on the adsorption energies and structures is discussed.

Abstract: This paper reports the results of a classical molecular dynamics (CMD) study of molecular water adsorption on MO2- and SrO-terminated SrMO3 (001) surfaces (M=Ti, Zr) at 300K with ½ML and 1ML coverage. Models of the force fields for the water–crystalline oxide interfaces have been proposed. These force fields describe the oxide–oxide, water–oxide and water–water interactions, as well as interactions within the water molecule itself. The water–water and flexible water intramolecular potentials have been adopted from Toukan and Rahman (Phys. Rev. B 31 (1985) 2643–2648). The results of CMD simulations of the structure of the water layers at the oxide surfaces are discussed in terms of the most probable configurations. The power spectra of the water hydrogen velocity autocorrelation functions have been calculated using the CMD trajectories. The calculated power spectra permit us to consider the vibrational modes of the different structural species formed by the water molecules at the oxide surfaces and to analyse the level of binding of these species, both between themselves and to the surface. [Copyright &y& Elsevier]

Abstract: First-principles calculations have been used to study the atomic structure, preferred sites and adsorption energies for water adsorption at different terminations of the cubic phase of perovskite-structured BaHfO3 and BaZrO3. By considering different initial positions of water molecules, the possibility of water dissociation has been investigated. It is demonstrated that the site selectivity and the form of adsorbed molecule can be affected by the choice of surface unit cell. Dissociative adsorption was found to be favorable for all surfaces in consideration. Hydroxylation of ZrO2- and HfO2-terminated surfaces is accomplished by a noticeable reconstruction of the surface structure of cubic phase towards the orthorhombic phase. Calculated atomic charges in bare and hydroxylated surfaces show that BaHfO3 crystal is slightly more ionic than BaZrO3. [ABSTRACT FROM AUTHOR]

Abstract: HF-DFT LCAO hybrid simulations on (001) and (110) surfaces of orthorhombic and (001) surface of cubic SrHfO3 perovskite are performed using a single slab model framework. PBE0 exchange-correlation functional is used for this study. The energy and crystal structure of bulk cubic and orthorhombic phases are calculated and compared. It is found that orthorhombic modification is more stable than cubic one by 24kJ mol–1 per formula unit. Calculated average surface energies and relaxation energies proved to be similar for all orthorhombic surfaces. Atomic displacements along the direction normal to the surface are primarily determined by the type of termination and weakly depend on the surface indices. Without symmetry constraining, cubic surfaces are unstable with respect to reconstruction to corresponding orthorhombic surfaces at T =0K. While the upright displacements of the topmost atoms are mainly due to additional distortions of the surface octahedra, the lateral atomic displacements are closely related to changing in surface group tilting. The approach for the analysis of surface octahedron tilting is proposed and applied to the relaxed orthorhombic surfaces of SrHfO3 perovskites. It is shown that the HfO5 group on the HfO2-termianted surfaces undergoes a considerable turn upon relaxation, resulting in alignment of Hf–O–Hf bonds to corresponding pseudo-cubic directions. [Copyright &y& Elsevier]

Abstract: Hybrid HF-DFT LCAO simulations of (001) surface properties and water adsorption on cubic SrZrO3 and SrTiO3 perovskites are performed using a single slab model framework. Three slab models with the different surface termination including 6–11 atomic planes were used for calculations. The effect of the symmetry reduction and the role of an extra atomic layer basis set have been considered for the bare surface slabs. The optimized structures and water adsorption energies have been calculated for the various types of surface coverage. It is shown that the formation of H-bonds between the water hydrogens and surface oxygens, as well as between the water molecules themselves, controls the structure of the water adsorption layers on the perovskite surfaces. Obtained results indicate that the dissociative type of water adsorption is the energetically more favourable for SrO-terminated zirconate surface than for similar titanate surface giving evidence to the more basic nature of oxygen atoms on SrO-terminated SrZrO3 surface. [Copyright &y& Elsevier]

Abstract: A simple procedure of 1D nanotubes (NT) construction based on the supercell of 2D (101) slab rolling and subsequent cylindrical coordinate system introduction is suggested. This procedure is applicable for any of five 2D lattices as well as both single- and multi-wall nanotubes provided that the chirality and translation vectors orthogonality condition is satisfied. The procedure suggested is applied to the centered rectangular 2D lattice, formed by (101) sheet of the bulk anatase. It is shown that (n, 0) and (0, m) nanotubes can be constructed by rolling an anatase (101) sheet along the and [010] directions respectively. The orthogonal to chirality vector translation vector does not exist for n ≠ m ≠0 general case. The first principles LCAO calculations of (n, 0) and (0, m) NT’s are made with hybrid HF/KS (PBE0) exchange-correlation functional for systems containing up to 180 atoms (n =6, 9, 12, 15; m =3−6). It is demonstrated that the energy band gap increases (from 4.7 to 5.4eV) when the NT radius changes from 3.61 to 9.92Å. The strain energy is larger for (n, 0) than for (0, m) nanotubes of a similar radius. The changes of the unit cell periodicity and radius of titania nanotubes after the structure optimization are negligible, however the atomic relaxations are noticeable. [Copyright &y& Elsevier]