76 research outputs found

    From symmetry to syntopy : a fuzzy-set approach to quasi-symmetric systems

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    Point symmetry is essentially a discrete concept, whereas molecular structures and their conformational changes display continuous features. Using the formalism of fuzzy-set theory, we propose a continuous extension of the symmetry concept for quasi-symmetric systems. For each point k of the reduced nuclear configuration space M of all N-atom systems having a specified stoichiometry, and for an energy criterion ε suggested by the statics or the dynamics of these systems, we define membership functions µi(k, ε) which generate 'syntopy' fuzzy subsets Si, in the metric space M ; these latter are used to obtain a continuous extension s(k, ε) of the symmetry point groups gi. Illustrations of the procedures used are given on simple examples, and applications of the new concept are outlined

    From quantum similarity measures to quantum analogy functors: tools for QShAR, quantitative shape-activity relations

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