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Shiv Nadar University

Center for Informatics

The atomic structures, growth behavior and electronic properties of (Al2O3)n, n = 1-10, clusters have been studied within the framework of density functional pseudopotential theory and generalized gradient approximation for the exchange-correlation energy. The lowest energy isomers of these clusters show preference for 4-membered Al 2O2 and 6-membered Al3O3 rings. There are 3-, 4- and 5-fold coordinated Al atoms and 2-, 3- and 4-fold coordinated oxygen atoms. The atomic structures have similarity with that of the $\gamma$-Al2O3 phase and the average coordinations of Al and O atoms in clusters are much lower from the values in the ground state of $\alpha$-Al2O3 (corundum structure). In general, isomers with cage structures lie significantly higher in energy compared with the lowest energy structures we have obtained. The bonding characteristics for clusters of different sizes is studied using Bader charge analysis. It is found that with increasing size, the charge transfer from Al atoms to oxygen increases toward the value in bulk. Further, the infrared (IR) and Raman spectra have been calculated. For n = 4, a comparison of the calculated IR spectra for a few isomers with the available experimental results on cation shows the possibility of the occurrence of a mixture of isomers in experiments. The Raman spectra of these isomers are, however, quite different. Therefore, it is suggested that measurements on Raman spectra could give a clear indication of the isomer present in experiments. {\textcopyright} 2011 American Chemical Society.

World University root node

Journal of Physical Chemistry C

Structural and electronic properties of (Al2O3) n clusters with n = 1-10 from first principles calculations

Ab initio calculations on ZnSe quantum dots (QDs) doped with one Mn atom predict a new nonstoichiometric magnetic magic Zn11MnSe13 structure in contrast to QDs of undoped ZnSe that are stoichiometric and exhibit magic behavior for ZnnSen with n = 13 and 34. Our results suggest that such doping would lead to a high abundance of only one specie (the magic QD) that would be produced preferentially. The stoichiometric Zn n-1MnSen QDs have a large magnetic moment of 5 $\mu$B that is predominantly localized on the Mn site. However, nonstoichiometic QD has a reduced magnetic moment of 3 $\mu$B due to strong covalent bonding of the Mn atom with the excess Se atom and a small gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Charging this magic QD with two electrons leads to a large HOMO-LUMO gap of 1.8 eV and 5 $\mu$B magnetic moment. These results together with calculations on Mn-doped n = 34 QD provide a possible growth mechanism of larger doped QDs and a new ground for understanding such QDs of compound semiconductors. {\textcopyright} 2011 American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Discovery of a nonstoichiometric Zn11MnSe13 magnetic magic quantum dot from ab initio calculations

Ab-initio calculations on graphene doped with boron nitride (BN) nanoribbons and patches show opening of a band gap in all cases. The smallest width of graphene in these hybrid layers controls the band gap that varies slowly around ∼0.75 eV when the width of graphene region is in the range of 2 to 5 zigzag chains. Most interestingly the band gap is direct in all the cases we have studied and nearly the same for different doping if the smallest graphene width is the same. These results show the possibility of ultrathin hybrid semiconductor graphene with band gap similar to silicon and an additional attractive feature that it is direct. {\textcopyright} 2011 American Physical Society.

Direct band gap opening in graphene by BN doping: Ab initio calculations

The atomic structure of Pd40Ni40P20 bulk metallic glass has been simulated using an ab initio molecular dynamics method with projector-augmented wave pseudopotentials for electron-ion interaction and generalized gradient approximation for exchange-correlation energy. The calculated extended x-ray absorption fine structure (EXAFS) spectra of Pd-K and Ni-K edges, the mass density and the electronic structure agree remarkably well with the available experimental data and the EXAFS spectra measured at the SPring-8 synchrotron radiation facility. Our results show that the atomic structure can be described in terms of P-centered polyhedra. There are no two P atoms that are nearest neighbors at this composition and this could be a reason for the observed optimal P concentration of about 20 at.%. The neighboring polyhedra share metal (M) atoms and form a polar covalently bonded random network of P-M-P favoring certain angles. The remaining M atoms act as metallic glue with a tendency of nanoscale clustering of Pd-Pd and Ni-Ni atoms. {\textcopyright} 2011 American Physical Society.

Atomic and electronic structure of Pd40Ni40P 20 bulk metallic glass from ab initio simulations

Elsevier

Nanosilicon

The field of nanoscience was pioneered in the 1980s with the groundbreaking research on clusters, which later led to the discovery of fullerenes. Handbook of Nanophysics: Clusters and Fullerenes focuses on the fundamental physics of these nanoscale materials and structures. Each peer-reviewed chapter contains a broad-based introduction and enhances understanding of the state-of-the-art scientific content through fundamental equations and illustrations, some in color. This volume covers free clusters, including hydrogen, bimetallic, silicon, metal and atomic clusters, as well as the cluster interactions. The expert contributors examine how carbon fullerenes are produced and how to characterize their stability. They discuss the structure, properties and behavior of carbon fullerenes, including the smallest possible fullerene: C20. The book also looks at inorganic fullerenes, such as boron fullerenes, silicon fullerenes, nanocones and onion-like inorganic fullerenes. Nanophysics brings together multiple disciplines to determine the structural, electronic, optical and thermal behavior of nanomaterials; electrical and thermal conductivity; the forces between nanoscale objects; and the transition between classical and quantum behavior. Facilitating communication across many disciplines, this landmark publication encourages scientists with disparate interests to collaborate on interdisciplinary projects and incorporate the theory and methodology of other areas into their work.

Clusters and Fullerenes

Automatically classifying ECG recordings for arrhythmia is difficult since even normal ECG signals exhibit irregularities, and learning algorithms suffer from class imbalance. We propose a hybrid SVM to combat class imbalance rampant in biomedical signals. Consequently, we significantly reduce the number patients falsely classified as normal. The Hybrid SVM is suitable for a variety of multiclass problems; here, we used the MIT-BIH Arrhythmia database, and the position and magnitude of local singularities as features. We enhance relevant singularity-driven Hölder features proposed earlier; while the use of these features results in higher accuracy, using the Hybrid SVM shows even more gains. Copyright © 2010 Inderscience Enterprises Ltd.

International Journal of Functional Informatics and Personalised Medicine

Hybrid Support Vector Machine for imbalanced data in multiclass arrhythmia classification

Scanning tunneling microscopy has been used to spatially image individual fluorofullerene C60F18 molecules on Si(111)-7×7 surface. The images have been interpreted with the help of ab initio calculations. C60F18 molecules interact with the surface with F atoms pointing down, whereas a large electric dipole moment of the molecule induces strong polarization on the surface but the charge transfer is small. It has been shown that during the time of image collection, some of the F atoms migrate from fluorofullerene molecule due to F binding energy on a Si surface being nearly twice the mean value on the C60 molecule. {\textcopyright} 2010 Taylor & Francis Group, LLC.

Fullerenes Nanotubes and Carbon Nanostructures

Adsorption and electronic structure of single C60F18 molecule on Si(111)-7×7 surface

We report from ab initio calculations a magic magnetic cage cluster of gold, Gd@ Au15, obtained by doping of a Gd atom in gold clusters. It has a highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.31 eV within the generalized gradient approximation that makes it a potential candidate for cancer therapy with an additional attractive feature that its large magnetic moment of 7 $\mu$B could be beneficial for magnetic resonance imaging. {\textcopyright} 2010 American Institute of Physics.

Fulltext

Applied Physics Letters

Gd@ Au15: A magic magnetic gold cluster for cancer therapy and bioimaging

We report results of ab initio calculations on (GaN)(n) nanoclusters with n = 12, 16, 22 and 24 using generalized gradient approximation (GGA) for the exchange-correlation energy. We find cage structures of GaN clusters to be lower in energy as compared to bulk fragments which have been fully optimized. Selected cages have been doped with Gd and Nd atoms by substituting Gd and Nd on Ga sites, respectively. The atomic structures of such doped nanoclusters have been optimized using spin-polarized GGA and by including all f electrons on the rare earth atoms. We find the doped nanoclusters to be magnetic with 7 mu(B) (3 mu(B)) magnetic moments when 1 Gd (Nd) atom is doped. When 2 Gd (Nd) atoms are substituted on different Ga sites, there is often a ferromagnetic coupling between the rare earth atoms, but we also find zero net magnetic moment in the nanocluster depending upon the separation between the doped atoms suggesting that both ferromagnetic and antiferromagnetic couplings may occur between the rare earth dopants.