Molecular dynamics characterization of void defects in crystalline (1,3,5-trinitro-1,3,5-triazacyclohexane)

Sylke Boyd, Jane S. Murray, Peter Politzer

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    Abstract

    In the context of a continuing investigation of factors that affect the sensitivities of energetic materials to detonation initiation, we have carried out a molecular dynamics characterization of void defects in crystalline (1,3,5-trinitro-1,3,5-triazacyclo-hexane). An empirical force field that is capable of handling flexible molecules in a pliable crystal was used. Voids ranging in size from 2 to 30 adjacent vacated sites were created in model lattices of 216 or 512 molecules. Energetic and geometric ground state properties were determined. The void formation energy per molecule removed was found to decrease from 50 kcal/mol for a single vacancy to about 23±2 kcal/mol for voids larger than one unit cell (8 molecules). Analysis of the local binding energies in the vicinity of a void reveals not only the expected decrease for molecules directly on the void surface but also a wide spread of values in the first 5-10 Å away from the surface; this includes some molecules with local binding energies significantly higher than in the defect-free lattice. Molecular conformational changes and reorientations begin to be found in the vicinities of voids larger than one unit cell. Thermal behavior investigated includes void and molecular diffusion coefficients and fluctuations in void size.

    Original languageEnglish (US)
    Article number204903
    JournalJournal of Chemical Physics
    Volume131
    Issue number20
    DOIs
    StatePublished - Dec 14 2009

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