We use density functional tight-binding (DFTB) theory to calculate the surface energies of two energetic crystals: monoclinic β-1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (β-HMX) and tetragonal pentaerythritol tetranitrate (PETN). The results are then employed to determine crystal shapes using the Bravais–Friedel–Donnay–Harker, attachment energy, and surface energy models. We find that energy-based models yield predictions in good agreement with experimental observations. Additionally, we propose a simple model that reframes surface energy as a measure of the lost intermolecular interactions during the formation of a surface from the bulk. The model accurately captures the results from the DFTB calculations and enables us to explain and predict surface energies as a function of the local molecular environment.

中文翻译：

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通过密度泛函紧结合计算对 β-1,3,5,7-四硝基-1,3,5,7-四唑辛烷和季戊四醇四硝酸酯进行表面研究及其对晶体形状的影响

我们使用密度泛函紧束缚（DFTB）理论来计算两种高能晶体的表面能：单斜晶系β-1,3,5,7-四硝基-1,3,5,7-四氮辛烷（β-HMX）和四方晶系季戊四醇四硝酸酯（PETN）。然后利用布拉维-弗里德尔-唐奈-哈克、附着能和表面能模型将结果用于确定晶体形状。我们发现基于能量的模型产生的预测与实验观察结果非常一致。此外，我们提出了一个简单的模型，该模型将表面能重新定义为从本体形成表面期间损失的分子间相互作用的度量。该模型准确地捕获了 DFTB 计算的结果，使我们能够解释和预测表面能作为局部分子环境的函数。