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Ab initio calculations have been performed on adsorption of H2O molecules on Ti-doped silicon clusters TiSin using the ultrasoft pseudopotential method within the generalized gradient approximation. Our results show that for n=13 and larger clusters adsorption of H2O on TiSin could be difficult due to low binding energies. All these clusters have cage structures with the metal atom surrounded by the silicon atoms. On the other hand, smaller clusters with n < 13 have the metal atom partially covered by Si atoms in a basket structure so that it is available for reaction with a water molecule. This leads to significantly higher binding energies of a water molecule on such clusters. These results are in excellent agreement with the available experimental data, which show significant decrease of H2O adsorption on clusters with n > 12.

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Physical Review B - Condensed Matter and Materials Physics

Water adsorption on Ti-doped silicon clusters

Keiso Kagaku Kyokaishi

Investigation of Atomic Structure of Si (313) 12x1 Reconstructed Surface by ab initio Calculations and STM Measurements.

Proceedings of Ⅻ International Symposium on Small Particles and Inorganic {\ldots}

Novel core-cage structures and ultra-stable behavior on nanoparticles of II-VI compound semiconductors

Nanoforms of silicon such as nanoparticles and nanowires have been attracting much attention and recent findings of novel metal encapsulated silicon clusters as well as nanotubes have opened up new avenues for the development of silicon nanostructures. We review these recent developments and discuss the findings of the metal encapsulated nanotubes of silicon and germanium using ab initio total energy calculations. These nanotubes are generally found to be metallic. The metalicity is not induced by the doping of metal atoms, though they stabilize silicon and germanium in tubular forms. Transition metal atoms such as Mn and Fe lead to nanotubes that are ferromagnetic making them interesting as nanomagnets. Antiferromagnetic and ferrimagnetic phases have also been obtained. A novel aspect of these magnetic nanotubes is the possibility of developing half-metallic nanotubes that could be interesting for nano-spintronics applications. Further possibilities of semiconducting silicon nanotubes are discussed. {\textcopyright} The Royal Society of Chemistry.

Fulltext

Journal of Materials Chemistry

Metal encapsulated nanotubes of silicon and germanium

A hybrid strategy of using (i) locally linear embedding for nonlinear dimensionality reduction of high dimensional data and (ii) support vector machines for classification of the resultant features is proposed as a robust methodology for process monitoring. Illustrative examples substantiate the methodology vis-à-vis current practice.

International Journal of Chemical Reactor Engineering

A hybrid methodology for on-line process monitoring

We report results of density functional theory calculations on three derivatives of the recently predicted hydrogenated silicon fullerene cluster Si20H20 using the B3PW91 hybrid exchange-correlation functional with the 6-311+G(d) basis set. The cluster has been exohedrally functionalized by replacing one of its H atoms with -CH2OH, -COOH and -CONH2. The resulting functionalized clusters have nearly the same HOMO-LUMO gaps as that of the perhydrogenated silicon fullerene leading to the possibility of developing new silicon fullerene-based molecules for medico-biological applications. The deprotonated Si20H 19(COO-) cluster displays a very large permanent dipole moment along with a strongly localized HOMO on its carboxyl group. {\textcopyright} 2003 Elsevier B.V. All rights reserved.

Chemical Physics Letters

Exohedral functionalization of the icosahedral cluster Si 20H20: A density functional theory study

Ab initio pseudopotential calculations of the atomic structures and magnetic behavior of Rhn (n≤15) clusters using the generalized gradient approximation for the exchange-correlation energy, reveal new lowest energy structures that are noncompact and have no atom at the center upto n=13, leading to a nonicosahedral growth. An eight-atom cluster has cubic structure and is magic. Some clusters beyond 13 atoms also do not have close packed structures due to some covalent character in the bonding. The calculated magnetic moments are generally lower and in better agreement with experiments than obtained before. Further studies on Ru13 and Pd13 clusters show that the lowest energy isomers of these clusters are also nonicosahedral. These findings of the novel behavior of technologically important transition metal clusters provide new ground for a better understanding and design of new catalysts.

Nonicosahedral growth and magnetic behavior of rhodium clusters

Endohedral silion fullerenes

This paper describes a robust support vector machines (SVMs) classification methodology, which can offer superior classification performance for important process engineering problems. The method incorporates efficient tuning procedures based on minimization of radius/margin and span bound for leave-one-out errors. An agent-based asynchronous teams (A-teams) software framework, which combines Genetic-Quasi-Newton algorithms for the optimization is highly successful in obtaining the optimal SVM hyper-parameters. The algorithm has been applied for classification of binary as well as multi-class real world problems. © 2003 Elsevier Ltd. All rights reserved.

Computers and Chemical Engineering

Support vector classification with parameter tuning assisted by agent-based technique

Magnetism in clusters having upto 15 atoms of non-magnetic element, Rh is studied using the ab initio ultrasoft pseudopotential method and generalized gradient approximation for the exchangecorrelation energy. The lowest energy structures are found to have no atom at the center upto n= 13 and have low symmetries. The well known icosahedral structure for 13 atoms does not have the lowest energy. A transition to more compact structures with an atom at the center occurs beyond 13 atoms. The calculated magnetic moments are in better agreement with experiments than obtained before. An H atom on these clusters favors a bridge side and generally reduces the magnetic moment.