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Role of stacking disorder in ice nucleation

机译：堆垛障碍在冰成核中的作用

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摘要

The freezing of water affects the processes that determine Earth's climate. Therefore, accurate weather and climate forecasts hinge on good predictions of ice nucleation rates(1). Such rate predictions are based on extrapolations using classical nucleation theory(1,2), which assumes that the structure of nanometre-sized ice crystallites corresponds to that of hexagonal ice, the thermodynamically stable form of bulk ice. However, simulations with various water models find that ice nucleated and grown under atmospheric temperatures is at all sizes stacking-disordered, consisting of random sequences of cubic and hexagonal ice layers(3-8). This implies that stacking-disordered ice crystallites either are more stable than hexagonal ice crystallites or form because of non-equilibrium dynamical effects. Both scenarios challenge central tenets of classical nucleation theory. Here we use rare-event sampling(9-11) and free energy calculations(12) with the mW water model(13) to show that the entropy of mixing cubic and hexagonal layers makes stacking-disordered ice the stable phase for crystallites up to a size of at least 100,000 molecules. We find that stacking-disordered critical crystallites at 230 kelvin are about 14 kilojoules per mole of crystallite more stable than hexagonal crystallites, making their ice nucleation rates more than three orders of magnitude higher than predicted by classical nucleation theory. This effect on nucleation rates is temperature dependent, being the most pronounced at the warmest conditions, and should affect the modelling of cloud formation and ice particle numbers, which are very sensitive to the temperature dependence of ice nucleation rates(1). We conclude that classical nucleation theory needs to be corrected to include the dependence of the crystallization driving force on the size of the ice crystallite when interpreting and extrapolating ice nucleation rates from experimental laboratory conditions to the temperatures that occur in clouds.
机译：水的冻结影响决定地球气候的过程。因此，准确的天气和气候预报取决于对冰成核率的良好预测（1）。这样的速率预测是基于使用经典成核理论（1,2）的外推法得出的，该理论假设纳米级冰晶的结构与六方冰（大体积冰的热力学稳定形式）的结构相对应。但是，通过各种水模型的模拟发现，在大气温度下成核和生长的冰在所有大小上都是无序堆积的，由立方和六边形冰层的随机序列组成（3-8）。这意味着堆积不规则的冰晶比六角形的冰晶更稳定，或者由于非平衡动力效应而形成。两种情况都挑战了经典成核理论的核心原则。在这里，我们使用稀疏事件采样（9-11）和自由能计算（12）以及mW水模型（13）表明，立方和六边形层混合的熵使堆积无序的冰成为微晶的稳定相，直至至少有100,000个分子。我们发现，在230开尔文处，无序堆垛的临界微晶每摩尔微晶比六方晶微晶稳定约14千焦耳，这使得它们的冰成核速率比经典成核理论所预测的高三个数量级。这种对成核速率的影响取决于温度，在最温暖的条件下最为明显，并且应影响云形成和冰粒数量的建模，这对冰成核速率的温度依赖性非常敏感（1）。我们得出的结论是，当解释和推断从实验实验室条件到云中温度的成核速率时，需要修正经典成核理论，以包括结晶驱动力对冰晶尺寸的依赖性。

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  • 来源
    《Nature》 |2017年第7679期|218-222|共5页
  • 作者

    Lupi Laura; Hudait Arpa; Peters Baron; Grunwald Michael; Mullen Ryan Gotchy; Nguyen Andrew H.; Molinero Valeria;

  • 作者单位

    Univ Utah, Dept Chem, Salt Lake City, UT 84112 USA;

    Univ Utah, Dept Chem, Salt Lake City, UT 84112 USA;

    Univ Calif Santa Barbara, Dept Chem Engn, Santa Barbara, CA 93106 USA|Univ Calif Santa Barbara, Dept Chem & Biochem, Santa Barbara, CA 93106 USA;

    Univ Utah, Dept Chem, Salt Lake City, UT 84112 USA;

    Univ Calif Santa Barbara, Dept Chem Engn, Santa Barbara, CA 93106 USA|Univ Calif Santa Barbara, Dept Chem & Biochem, Santa Barbara, CA 93106 USA;

    Univ Utah, Dept Chem, Salt Lake City, UT 84112 USA;

    Univ Utah, Dept Chem, Salt Lake City, UT 84112 USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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