Why don't we find more polymorphs?
Why don't we find more polymorphs?
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DOI：
10.1107/s2052519213018861
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发表时间：
2013-08-01
影响因子：
1.9
通讯作者：
Price, Sarah L.
中科院分区：
文献类型：
--
作者：
Price, Sarah L.
晶体结构预测（CSP）研究不仅限于寻找最热力学稳定的晶体结构，而且在理解多态性方面发挥着宝贵的作用，正如跨学科研究所表明的那样，晶体能量景观已经通过实验和计算进行了探索。CSP通常比已知的多晶晶产生更多热力学上合理的晶体结构。本文说明了一些原因：因为(i)计算中的近似，特别是忽略了热效应（见1.1）；（ii）成核和生长过程中的分子重排（见1.2）；（iii）观察到的固态结构表现出动态或静态无序、堆叠缺陷、其他缺陷，或者不是结晶性的，因此代表了不止一种计算结构（见1.3）；（iv）结构相对于其他分子组成是亚稳的（见1.4）；(v)尚未进行正确的结晶实验（见1.5）或（vi）无法进行（见1.6），以及（vii）未检测到多晶型或未对其进行结构表征的可能性（见1.7）。因此，我们只能期望对多态性有一个一般的预测理论，因为这似乎需要对所有可能的多组分结晶所涉及的动力学因素有一个定量的理解。对于一个特定的分子，晶体能量景观的分析显示了其结晶行为的潜在复杂性。
Crystal structure prediction (CSP) studies are not limited to being a search for the most thermodynamically stable crystal structure, but play a valuable role in understanding polymorphism, as shown by interdisciplinary studies where the crystal energy landscape has been explored experimentally and computationally. CSP usually produces more thermodynamically plausible crystal structures than known polymorphs. This article illustrates some reasons why: because (i) of approximations in the calculations, particularly the neglect of thermal effects (see 1.1); (ii) of the molecular rearrangement during nucleation and growth (see 1.2); (iii) the solid-state structures observed show dynamic or static disorder, stacking faults, other defects or are not crystalline and so represent more than one calculated structure (see 1.3); (iv) the structures are metastable relative to other molecular compositions (see 1.4); (v) the right crystallization experiment has not yet been performed (see 1.5) or (vi) cannot be performed (see 1.6) and the possibility (vii) that the polymorphs are not detected or structurally characterized (see 1.7). Thus, we can only aspire to a general predictive theory for polymorphism, as this appears to require a quantitative understanding of the kinetic factors involved in all possible multi-component crystallizations. For a specific molecule, analysis of the crystal energy landscape shows the potential complexity of its crystallization behaviour.