DFT periodic calculations were carried out in order to gain more insight in relation with the stability of the (0 0 1) and (1 0 0) surfaces of the hexagonal WO. These surfaces display an uncommon instability which could be attributed to their high polarity and the intrinsic instability problems of the hexagonal phase. Indifferently of the slab thickness, the internal structure of the slabs suffers distortion even at levels of a total loss of the hexagonal phase structure. Stoichiometric and non-stoichiometric O reconstructions do not seem to be practical mechanisms to solve the instability problem of these surfaces, leaving only the partial frozen slabs an efficient way to model the hexagonal (0 0 1) and (1 0 0) surfaces. However, the surface energy of these surfaces is dependent of the optimized layers instead of the frozen ones. Results obtained for the CO adsorption on the (0 0 1) surface showed that a model with six layers and two internal layers frozen to the atomic position of the bulk structure is enough to reach the structural and energetic stability of the CO adsorption.

中文翻译：

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从周期性DFT角度发现六方WO3表面稳定性的根源


为了更深入地了解六边形 WO 的 (0 0 1) 和 (1 0 0) 表面的稳定性，进行了 DFT 周期性计算。这些表面表现出罕见的不稳定性，这可能归因于它们的高极性和六方相的固有不稳定性问题。无论板坯厚度如何，即使在六方相结构完全丧失的水平下，板坯的内部结构也会发生变形。化学计量和非化学计量 O 重建似乎不是解决这些表面不稳定问题的实用机制，仅留下部分冻结板是模拟六边形 (0 0 1) 和 (1 0 0) 表面的有效方法。然而，这些表面的表面能取决于优化层而不是冻结层。 (0 0 1) 表面上的 CO 吸附结果表明，具有六层和两个内层的模型冻结到块体结构的原子位置足以达到 CO 吸附的结构和能量稳定性。