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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Quantum Molecular Dynamics Simulations of Low-Temperature High Energy Density Matter: Solid p-H_2/Li and p-H_2/B
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Quantum Molecular Dynamics Simulations of Low-Temperature High Energy Density Matter: Solid p-H_2/Li and p-H_2/B

机译：低温高能量密度物质：固体p-H_2 / Li和p-H_2 / B的量子分子动力学模拟

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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 A 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.
机译：通过在4 K和零外部压力下采用路径积分分子动力学（PIMD）和质心分子动力学（CMD）模拟研究了固体对氢中捕获的原子杂质Li和B的亚稳性。从由1440个粒子组成的纯固体氢开始，通过在取代缺陷位点用杂质原子代替氢分子来制备掺杂体系。然后针对各种浓度计算热力学量，并监控系统的稳定性。对于锂的情况，包含2.5摩尔％掺杂剂的体系在热力学量收敛的情况下保持亚稳态，但是包含3.3摩尔％或更多的掺杂剂的体系变得不稳定。对于硼而言，在模拟的时间范围内，含有高达15 mol％掺杂剂的系统保持亚稳态，而含有25 mol％掺杂剂的系统则不会。这些结果提供了从亚稳态到整体不稳定性过渡的证据，并粗略估计了两种原子物种的最大掺杂密度。计算表明，掺硼系统比掺锂系统具有更高的杂质浓度。对于6.25mol％的硼杂质，计算出较长时间的本征硼反应速率。计算平均力的量子质心势（PMF），然后使用路径积分量子跃迁状态理论（PI-QTST）估计重组反应速率。 PI-QTST计算表明，在此浓度下，硼二聚体重组的过渡态在5.39 A分离处发生，其自由能垒为360 +-36K。计算出的内在重组反应速率约为8 * 10〜（-27） s〜（-1）。该结果表明，硼重组反应的总反应速率可能受到固有的重组速率的限制，而不是受到杂质的自我扩散的限制。还发现，在该浓度下，硼的初始反应仅引起其他硼杂质的局部重组，而不引起整体不稳定。还通过CMD模拟研究了单个硼对反应对系统其余部分的动力学影响。这些模拟表明，二聚体重组释放的能量不会导致固体整体熔化。

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