Victor A Ranea - Academia.edu (original) (raw)
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Ab initio density-functional theory has been used to investigate the adsorption of a single H 2 O... more Ab initio density-functional theory has been used to investigate the adsorption of a single H 2 O molecule on the Ag͕111͖ surface. A series of geometry optimizations on a slab model has allowed us to identify a preferred energy minimum and several stationary points in the potential-energy surface of this system. The most stable adsorption position for water corresponds to the atop site, with the dipole moment of the molecule oriented nearly parallel to the surface. The electronic structure of several H 2 O-Ag clusters has been compared to results obtained by the extended slab calculations. The agreement found for several properties ͑binding energy, tilt angle of the dipole moment of water, and interatomic distances͒ provides evidence for the local nature of the water-metal atop interaction. The covalent contribution to the weak H 2 O-Ag bond is found to be an important one.
Density functional theory has been used to investigate the adsorption and diffusion of H 2 O on A... more Density functional theory has been used to investigate the adsorption and diffusion of H 2 O on Al͕100͖. The favored adsorption site for H 2 O is the atop site with a binding energy of ϳ350 meV. H 2 O binds only very weakly at bridge sites and does not adsorb at fourfold hollow sites. The activation energies for H 2 O diffusion depend on the specific orientation of the H 2 O molecule on the surface and range from 307-327 meV. We show that the barriers for H 2 O diffusion are consistently larger than the difference in adsorption energies between H 2 O at the most stable ͑atop͒ and next most stable ͑bridge͒ adsorption sites.
Based on the results of density functional theory calculations, a novel mechanism for the diffusi... more Based on the results of density functional theory calculations, a novel mechanism for the diffusion of water dimers on metal surfaces is proposed, which relies on the ability of H bonds to rearrange through quantum tunneling. The mechanism involves quasifree rotation of the dimer and exchange of H-bond donor and acceptor molecules. At appropriate temperatures, water dimers diffuse more rapidly than water monomers, thus providing a physical explanation for the experimentally measured high diffusivity of water dimers on Pd{111} [Mitsui et al.
Diffusion barriers for a cluster of three water molecules on Pd\{111\} have been estimated from a... more Diffusion barriers for a cluster of three water molecules on Pd\{111\} have been estimated from ab-initio Density Functional Theory. A model for the diffusion of a cluster of three water molecules (trimer) based in rotations yields a simple explanation of why the cluster can diffuse faster than a single water molecule by a factor approx102\approx 10^{2}approx102.\cite{salmeron1}
This model is based on the differences between the adsorption geometry for the three molecules forming the trimer. One member interacts strongly with the surface and sits closer to the surface (d) while the other two interact weakly and stay at a larger separation from the surface (u). The trimer rotates nearly freely around the axis determined by the d-like monomer.
Translations of the whole trimer imply breaking the strong interaction of the d-like molecule with the surface with a high energy cost. Alternatively, thermal fluctuations can exchange the position of the molecule sitting closer to the surface with a lower energetic cost. Rotations around different axis yield a diffusion mechanism where the strong interaction is maintained along the diffusion path, therefore lowering the effective activation barrier.
Ab initio density-functional theory has been used to investigate the adsorption of a single H 2 O... more Ab initio density-functional theory has been used to investigate the adsorption of a single H 2 O molecule on the Ag͕111͖ surface. A series of geometry optimizations on a slab model has allowed us to identify a preferred energy minimum and several stationary points in the potential-energy surface of this system. The most stable adsorption position for water corresponds to the atop site, with the dipole moment of the molecule oriented nearly parallel to the surface. The electronic structure of several H 2 O-Ag clusters has been compared to results obtained by the extended slab calculations. The agreement found for several properties ͑binding energy, tilt angle of the dipole moment of water, and interatomic distances͒ provides evidence for the local nature of the water-metal atop interaction. The covalent contribution to the weak H 2 O-Ag bond is found to be an important one.
Density functional theory has been used to investigate the adsorption and diffusion of H 2 O on A... more Density functional theory has been used to investigate the adsorption and diffusion of H 2 O on Al͕100͖. The favored adsorption site for H 2 O is the atop site with a binding energy of ϳ350 meV. H 2 O binds only very weakly at bridge sites and does not adsorb at fourfold hollow sites. The activation energies for H 2 O diffusion depend on the specific orientation of the H 2 O molecule on the surface and range from 307-327 meV. We show that the barriers for H 2 O diffusion are consistently larger than the difference in adsorption energies between H 2 O at the most stable ͑atop͒ and next most stable ͑bridge͒ adsorption sites.
Based on the results of density functional theory calculations, a novel mechanism for the diffusi... more Based on the results of density functional theory calculations, a novel mechanism for the diffusion of water dimers on metal surfaces is proposed, which relies on the ability of H bonds to rearrange through quantum tunneling. The mechanism involves quasifree rotation of the dimer and exchange of H-bond donor and acceptor molecules. At appropriate temperatures, water dimers diffuse more rapidly than water monomers, thus providing a physical explanation for the experimentally measured high diffusivity of water dimers on Pd{111} [Mitsui et al.
Diffusion barriers for a cluster of three water molecules on Pd\{111\} have been estimated from a... more Diffusion barriers for a cluster of three water molecules on Pd\{111\} have been estimated from ab-initio Density Functional Theory. A model for the diffusion of a cluster of three water molecules (trimer) based in rotations yields a simple explanation of why the cluster can diffuse faster than a single water molecule by a factor approx102\approx 10^{2}approx102.\cite{salmeron1}
This model is based on the differences between the adsorption geometry for the three molecules forming the trimer. One member interacts strongly with the surface and sits closer to the surface (d) while the other two interact weakly and stay at a larger separation from the surface (u). The trimer rotates nearly freely around the axis determined by the d-like monomer.
Translations of the whole trimer imply breaking the strong interaction of the d-like molecule with the surface with a high energy cost. Alternatively, thermal fluctuations can exchange the position of the molecule sitting closer to the surface with a lower energetic cost. Rotations around different axis yield a diffusion mechanism where the strong interaction is maintained along the diffusion path, therefore lowering the effective activation barrier.