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Quantum Molecular Dynamics Simulations of Low-Temperature High Energy Density Matter:  Solid p-H2/Li and p-H2/B

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Department of Chemistry and Henry Eyring Center for Theoretical Chemistry, University of Utah, 315 S. 1400 E. Rm Dock, Salt Lake City, Utah 84112-0850
Cite this: J. Phys. Chem. A 1999, 103, 47, 9512–9520
Publication Date (Web):October 30, 1999
Copyright © 1999 American Chemical Society

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    The metastability of atomic impurities, Li and B, trapped in solid parahydrogen is studied by employing path integral molecular dynamics (PIMD) and centroid molecular dynamics (CMD) simulations at 4 K and zero external pressure. Starting from pure solid hydrogen consisting of 1440 particles, doped systems are prepared by substituting impurity atoms for hydrogen molecules at substitutional defect sites. For various concentrations, thermodynamic quantities are then calculated and the stability of the systems is monitored. For the case of lithium, systems containing 2.5 mol % dopants remain metastable with convergent thermodynamic quantities, but systems with 3.3 mol % or more dopants become unstable. For the case of boron, systems containing as high as 15 mol % dopants remain metastable on the time scale of the simulation, while systems with 25 mol % dopants do not. These results provide evidence of the transition from metastability to global instability and a rough estimate of the maximum doping density of the two atomic species. The calculations show that boron-doped systems have the potential to achieve a higher impurity concentration than lithium-doped systems. The intrinsic boron reaction rate at longer times was calculated for 6.25 mol % of boron impurities. The quantum centroid potential of mean force (PMF) was calculated and then the recombination reaction rate was estimated using path integral quantum transition state theory (PI-QTST). The PI-QTST calculation suggests that the transition state for boron dimer recombination at this concentration occurs at 5.39 Å separation and its free energy barrier is 360 ± 36 K. The calculated intrinsic recombination reaction rate is approximately 8 × 10-27 s-1. This result suggests that the overall reaction rate of boron recombination reaction may be limited by the intrinsic recombination rate rather than by self-diffusion of the impurities. It is also found that the initial reaction of boron induces only local recombination of other boron impurities at this concentration and not a global instability. The dynamical effect of a single boron pair reaction on the rest of the system has also been studied by CMD simulations. These simulations show that the energy release from the dimer recombination does not lead to global melting of the solid.

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    Cited By

    This article is cited by 13 publications.

    1. Francesco Paesani, Sotiris S. Xantheas and Gregory A. Voth . Infrared Spectroscopy and Hydrogen-Bond Dynamics of Liquid Water from Centroid Molecular Dynamics with an Ab Initio-Based Force Field. The Journal of Physical Chemistry B 2009, 113 (39) , 13118-13130.
    2. Stephen Bates. Stable High Concentration Matrix Isolation of High Energy Species. 2006
    3. Qian Wang, Millard H. Alexander. Path-integral Monte Carlo simulation of the recombination of two Al atoms embedded in parahydrogen. The Journal of Chemical Physics 2006, 124 (3)
    4. Eitan Geva, Seogjoo Jang, Gregory A. Voth. Quantum Rate Theory: A Path Integral Centroid Perspective. 2005, 1691-1712.
    5. Dina T Mirijanian, Millard H Alexander, Gregory A Voth. Path integral molecular dynamics simulation of solid para-hydrogen with an aluminum impurity. Chemical Physics Letters 2002, 365 (5-6) , 487-493.
    6. Qian Wang, Millard H. Alexander, Jennifer R. Krumrine. An ab initio based model for the simulation of multiple 2P atoms embedded in a cluster of spherical ligands, with application to Al in solid para -hydrogen. The Journal of Chemical Physics 2002, 117 (11) , 5311-5318.
    7. F. Vigliotti, A. Cavina, Ch. Bressler, B. Lang, M. Chergui. Structural dynamics in quantum solids. I. Steady-state spectroscopy of the electronic bubble in solid hydrogens. The Journal of Chemical Physics 2002, 116 (11) , 4542-4552.
    8. Nicholas Blinov, Pierre-Nicholas Roy. An effective centroid Hamiltonian and its associated centroid dynamics for indistinguishable particles in a harmonic trap. The Journal of Chemical Physics 2002, 116 (12) , 4808.
    9. Majed Chergui. Structural dynamics in quantum solids. Comptes Rendus de l'Académie des Sciences - Series IV - Physics 2001, 2 (10) , 1453-1467.
    10. Nicholas Blinov, Pierre-Nicholas Roy. Operator formulation of centroid dynamics for Bose–Einstein and Fermi–Dirac statistics. The Journal of Chemical Physics 2001, 115 (17) , 7822-7831.
    11. Y.M. Ma, T. Cui, G.T. Zou. Isotope effects on the absorption spectrum of Li in solid hydrogens under high pressures. Chemical Physics Letters 2001, 343 (5-6) , 604-612.
    12. Y. M. Ma, T. Cui, G. T. Zou. Effects of pressure on the trapping site structures and absorption spectra of Li in solid H2: A path integral Monte Carlo study. The Journal of Chemical Physics 2001, 114 (7) , 3092-3104.
    13. Jennifer R. Krumrine, Soonmin Jang, Millard H. Alexander, Gregory A. Voth. Quantum molecular dynamics and spectral simulation of a boron impurity in solid para -hydrogen. The Journal of Chemical Physics 2000, 113 (20) , 9079-9089.

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