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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 4000-4009 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work, we present a simple approach for devising order parameters (OPs) for atomic systems based on pattern recognition techniques. It exploits the fact that all crystalline substances are characterized by a unique "signature" cell (SC) which is constructed using a central atom and its nearest NSC neighbors in a given crystal. The algorithm measures the local degree of similarity between a SC and the system to be analyzed. The best fit of a SC to NSC atoms surrounding a given atom in the system is determined by maximizing a fictitious energy of binding among those atoms and the SC atoms. The fictitious potential energy is designed to give maximum attractive energy for maximum overlap. The maximum binding energy of interaction attained in this process is used as a measure of similarity between the crystal structure and the system (i.e., as an OP). The proposed method provides a unified and intuitive approach for constructing relevant OPs for a given system. We used these OPs to characterize the order of different phases in the Lennard-Jones system and in a model silicon system. It is shown that these novel OPs give a more complete description and a better understanding of the structural order in amorphous silicon than conventional OPs. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7957-7966 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Virtual Gibbs ensembles (VGEs), a class of pseudo-ensemble Monte Carlo methods, are specialized in this work to simulate phase equilibrium for systems for which conventional direct methods (such as two-box Gibbs ensembles and one-box interfacial ensembles) are inadequate. It is shown that by removing the mass/volume balance constraints of conventional Gibbs ensembles, the resulting VGEs can be used to effectively simulate systems wherein (a) the number of molecules or the composition of one of the phases is to be kept constant and (b) the initial choices for the volume and number of molecules would preclude direct methods to convergence to a stable two-phase state. Applications of VGEs are presented for the simulation of vapor–liquid, vapor–solid, and liquid–solid equilibrium in single component systems and multicomponent sorption equilibria of gases in polymer melts. VGE simulations of solid–fluid coexistence entail the combination of elements of both interfacial ensembles and Gibbs ensembles. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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