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Shiv Nadar University

Center for Informatics

Using ab initio pseudopotential plane wave method and generalized gradient approximation for the exchange and correlation energy, we report the finding of high spin ground state of (formula presented) cluster in accordance with the Hund's rule of maximum spin at half-filling. It has perfect icosahedral symmetry and a magnetic moment of (formula presented) forming an open shell superatom. Further studies of its interaction with an Al atom have led to an electronically closed shell magic cluster with 1.68 eV highest occupied–lowest unoccupied molecular orbital (HOMO-LUMO) gap such that the added Al atom is incorporated within the cage around the Cu atom. {\textcopyright} 2001 The American Physical Society.

World University root node

Physical Review B - Condensed Matter and Materials Physics

Hund's rule in metal clusters: Prediction of high magnetic moment state of (formula presented) from first-principles calculations

Ab initio molecular-dynamics studies on SrN (N = 2–35, 55 and 147) clusters show d electron induced icosahedral growth. There is a gradual increase in the hybridization between the sp and d states as well as the metallization of clusters as the size grows. For Sr147, the highest occupied and lowest unoccupied molecular orbital gap becomes vanishingly small. The nonmetal-metal transition is found to occur more prominently along the close-packed directions from the center to the 12 vertices with an oscillatory behavior of the bond length. However, in other directions, there is a monotonic expansion as one goes from the center to the surface of the cluster. This is in contrast to contraction known in other metal clusters but agrees with the interlayer expansion found on the surfaces of divalent metals. {\textcopyright} 2001 The American Physical Society.

Evolution of electronic states and abnormal multishell relaxations in strontium clusters

We investigate the onset of chaotic resonance (CR) behavior by studying the dynamics of chaotically driven bistable systems near the crisis bifurcation point. Our analysis reveals the existence and identification of a characteristic natural frequency associated with the dynamics of the system confirming that classical resonance is responsible for CR. We also classify the different routes via which CR can originate. The ability to manipulate the route to CR can be of importance in developing technological applications. © 2000 Elsevier Science Ltd. All rights reserved.

Applied Mathematics Letters

Onset of resonance in chaotically driven systems

The Taboo search framework provides a simple and effective procedure for solving global optimization problems involving continuous functions. This novel algorithm handles both constrained and unconstrained functions very well and can be successfully used for large-scale process optimization.

Chemical Engineering Research and Design

Taboo search algorithm for continuous function optimization

An ant colony optimization framework has been compared and shown to be a viable alternative approach to other stochastic search algorithms. The algorithm has been tested for variety of different benchmark test functions involving constrained and unconstrained NLP, MILP, and MINLP optimization problems. This novel algorithm handles different types of continuous functions very well and can be successfully used for large-scale process optimization. An ant colony optimization framework has been compared and shown to be a viable alternative approach to other stochastic search algorithms. The algorithm has been tested for variety of different benchmark test functions involving constrained and unconstrained NLP, MILP, and MINLP optimization problems. This novel algorithm handles different types of continuous functions very well and can be successfully used for large-scale process optimization.

Industrial and Engineering Chemistry Research

Ant colony approach to continuous function optimization

Most stable structures and physical properties are studied for silicon-doped (Formula presented) and (Formula presented) clusters using the ab initio molecular-dynamics method within the framework of a plane-wave pseudopotential approach and the local density as well as the generalized gradient approximations. The lowest energy structures of the undoped clusters are found to be Jahn-Teller distorted icosahedron, double icosahedron and decahedron, respectively. Substitutional doping with a Si impurity makes these clusters electronically closed shell and leads to a large gain in the binding energy, which decreases with an increase in the cluster size in a nonmonotonic way. The heat of solution of a Si atom in clusters is found to be exothermic as compared to endothermic behavior in bulk aluminum. Further, a Si impurity is found to stabilize the (Formula presented) cluster in cuboctahedral structure. However, a capped icosahedron as well as a double icosahedron are found to be nearly degenerate with about 1.77 eV higher binding energy. For (Formula presented) the decahedral isomer has the lowest energy with a highest-occupied lowest-unoccupied molecular-orbital gap of 0.82 eV. It is also found to be very stable when heated at 700 K. Similar results are likely to hold in the case of doping with germanium. We discuss the significance of these results for the understanding of the stability of silicon-doped quasicrystals. {\textcopyright} 2000 The American Physical Society.

Silicon-doped icosahedral, cuboctahedral and decahedral clusters of aluminum

Advances in Cluster Science

This paper presents a new co-operative search approach, the ant colony optimisation paradigm, for the optimal design of batch chemical processes and illustrates it by solving (1) the combinatorial optimisation problem of multiproduct batch scheduling and (2) the continuous function optimisation problem for the design of multiproduct batch plant with single product campaigns and horizon constraints. The ant algorithm is simple to implement and results of the case studies show its ability to provide speedy and accurate solutions. (C) 2000 Elsevier Science Ltd.