Exploring the High-Pressure Polymorphs of Flexible Molecules by Crystal Structure Prediction: A Case of 1,3,5-Trinitro-1,3,5-Triazinane
Exploring the High-Pressure Polymorphs of Flexible Molecules by Crystal Structure Prediction: A Case of 1,3,5-Trinitro-1,3,5-Triazinane
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DOI：
10.1021/acs.cgd.3c00709
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发表时间：
2023-12
期刊：
影响因子：
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通讯作者：
Chaoyu Wang;Chaoyang Zhang;Bo You;Xianggui Xue
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文献类型：
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作者：
Chaoyu Wang;Chaoyang Zhang;Bo You;Xianggui Xue
含能化合物在使用过程中经常受到高压的影响，因此研究其高压多晶型对评价其性能具有重要意义。为了模拟实际应用中的含能晶体，采用组合方法对1，3，5-三硝基-1，3，5-三嗪烷（RDX）在常压和高压下的晶体结构进行了预测。也就是说，我们首先通过考虑RDX分子的柔性来修改力场（FF），以初步筛选出在普通条件下最有利的晶体结构，随后，色散校正密度泛函理论（DFT-D）方法被应用于在普通和高压条件下对结构进行细化和排序。因此，所有四个多晶型的RDX与实验确定的晶体结构被再现。除了β-RDX相对较低的排名外，α-（0 GPa时为1）、ε-和γ-RDX（5 GPa时分别为3和1）在相对能源格局中排名非常高。β-RDX的能量等级较低，表明其形成过程可能是动力学主导的。此外，一个潜在的高压形式，推定的η-RDX，被确定为它的等级1和2的压力范围内约2.3至3.5 GPa和在5 GPa，分别，需要进一步的实验验证。我们的工作验证了改进的FF和DFT-D组合方法的CSP，无论是在压力加载或没有。
Exploring the high-pressure polymorphs of energetic compounds is of great interest in evaluating their performances since they always suffer from high pressure in service. We conducted crystal structure prediction (CSP) of 1,3,5-trinitro-1,3,5-triazinane (RDX) at ambient and high pressures by a combined method to emulate energetic crystals in practical use. That is, we first modified a force field (FF) by considering the flexibility of the RDX molecule to primarily screen out the most energetically favored crystal structures under common conditions, and subsequently, the dispersion-corrected density functional theory (DFT-D) method was applied to refine and rank the structures under common and high-pressure conditions. Thereby, all four polymorphs of RDX with experimentally determined crystal structures are reproduced. Apart from the relatively low ranking of β-RDX, α- (1 at 0 GPa), ε-, and γ-RDX (3 and 1 at 5 GPa, respectively) rank very high in the relative energy landscape. The inferiority of the energy ranking of β-RDX suggests a possible kinetic domination in formation. Moreover, a potential high-pressure form, putative η-RDX, is identified as it ranks 1 and 2 in a pressure range of about 2.3 to 3.5 GPa and at 5 GPa, respectively, and needs further experimental verification. Our work validates the modified FF and DFT-D combined method to CSP, whether under pressure loading or not.