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Shiv Nadar University

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APS March Meeting Abstracts 2003, P31.

All-electron GW quasiparticle energies of small silicon clusters

The European Physical Journal D

Structures and stability of Al 7 C and Al 7 N clusters

Chemical physics letters 363 (3-4)

M@ Si16, M= Ti, Zr, Hf: $\pi$ conjugation, ionization potentials and electron affinities

Biotransformation of sucrose-based medium to polyols has been reported for the first time using osmophilic yeast, Hansenula anomala. A new, real coded evolutionary algorithm was developed for optimization of fermentation medium in parallel shake-flask experiments. By iteratively employing the nature-inspired techniques of selection, crossover, and mutation for a fixed number of generations, the algorithm obtains the optimal values of important process variables, namely, inoculum size and sugar, yeast extract, urea, and MgSO4 concentrations. Maximum polyols yield of 76.43% has been achieved. The method is useful for reducing the overall development time to obtain an efficient fermentation process.

Applied Biochemistry and Biotechnology - Part A Enzyme Engineering and Biotechnology

Optimization of media by evolutionary algorithms for production of polyols

We present results of first principles electronic structure calculations on (10,10) and (12,12) single wall carbon nanotube bundles under hydrostatic pressure using ultrasoft pseudopotential plane wave method and local density approximation for the exchange-correlation energy. It is found that the (10,10) bundles show a structural transformation of nanotubes from cylindrical to an oval shape accompanied by a transition from a near hexagonal to a monoclinic lattice. The (12,12) nanotubes are, however, commensurate with the underlying hexagonal lattice and there is only a polygonization to hexagonal shape of the nanotubes with increasing pressure accompanied by a reduction in the lattice constant. Similar results hold for zig-zag nanotubes also. This would explain the conflicting results obtained from experiments. Effects of pressure on the electronic structure are discussed. {\textcopyright} 2002 Elsevier Science B.V. All rights reserved.

Physica B: Condensed Matter

Structural and electronic transitions in single wall carbon nanotube bundles under pressure

Reviews of Modern Quantum Chemistry

Novel Metal Encapsulated Caged Clusters of Silicon

Metal (M)-encapsulated clusters of Ge and Sn, Zn@Ge12 and Cd@Sn12, are obtained from total energy calculations using ab initio pseudopotential plane wave method and generalized gradient approximation for the exchange-correlation energy. These have perfect icosahedral symmetry and large highest occupied-lowest unoccupied molecular orbital gap of about 2 eV. It lies in the optical region and makes these species attractive for cluster assembled optoelectronic materials. Calculations on silicon clusters doped with Be show a different behavior. {\textcopyright} 2002 American Institute of Physics.

Fulltext

Applied Physics Letters

Metal-encapsulated icosahedral superatoms of germanium and tin with large gaps: Zn@Ge12 and Cd @Sn12

Journal of Chemical Physics

Fragmentation of small tin cluster ions (Snx+: x = 4-20) in the low-energy collisions with a highly oriented pyrolytic graphite surface

This paper introduces a method for constrained optimization using a modified multi-objective algorithm. The algorithm treats the constraints as objective functions and handles them using the concept of Pareto dominance. The population members are ranked by two different ways: first ranking is based on objective function value and the second ranking is based on Pareto dominance of the population members. The maintenance of elite lists for both rankings facilitates preservation of potentially superior solutions. A range of problems including non-linear programming and mixed integer non-linear programming has been solved to test the efficacy of the proposed algorithm. The algorithm effectively handles constraints encountered in both small-scale and large-scale optimization problems. The performance of the algorithm compares favourably with existing evolutionary and heuristic approaches. ® 2002 Elsevier Science Ltd. All rights reserved.

Computers and Chemical Engineering

Solution of constrained optimization problems by multi-objective genetic algorithm

Ab initio calculations on (10,10) and (12,12) single-wall carbon-nanotube bundles show that the nature of the phase transformation under hydrostatic pressure is determined by the symmetry of the nanotubes. Bundles of (10,10) nanotubes that are incommensurate with the hexagonal lattice, have small deviations from hexagonal symmetry of the lattice even at zero pressure. A transition to monoclinic structure is obtained at about 1 GPa within the generalized gradient approximation such that the nanotubes transform to an oval shape. However, in the local-density approximation the monoclinic phase is retained even at zero pressure once the transformation has occurred. Bundles of (12,12) nanotubes are commensurate with the hexagonal symmetry of the lattice and show no transition even up to 6 GPa pressure except for a polygonization of the initially cylindrical nanotubes into a hexagonal shape. These results would resolve the contradictory conclusions obtained from experiments. {\textcopyright} 2002 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Symmetry-driven phase transformations in single-wall carbon-nanotube bundles under hydrostatic pressure