Recently, it was demonstrated that the conductivity of wurzite (wz) ZnO bicrystal samples containing $\left\{0001\right\}$ inversion domain boundaries (IDB) can be massively and reversibly tuned by mechanical loading. As a step towards a detailed microscopic understanding of this effect, we systematically investigate the atomic structure and chemical composition of such IDBs using density functional theory calculations. In total, 92 model geometries that differ in structure and/or chemical composition are constructed, optimized, and compared thermodynamically. The lack of higher symmetries in wz ZnO prohibits a straightforward calculation of individual grain boundary (GB) excess energies. However, we show that, in nonperiodic slab models of wz $\left\{0001\right\}$ IDBs, the additional surface contribution to the total energy may be approximated by that of corresponding zincblende (zb) surfaces; the latter can be obtained by a series of prism calculations. Subtracting these surface energies allows us to construct absolute GB energy diagrams for wz IDBs and compare their thermodynamic stability with other GBs known from the literature. We find that thermodynamically favored IDBs are characterized by fully (4-fold) coordinated atoms and possess relatively low excess energies that range from 45 to $95\mathrm{meV}/{\AA }^2$, depending on the termination (Zn/Zn or O/O) of the IDB and the exchange-correlation functional used in the calculation (LDA, GGA, or $\text{GGA}+U$). The electronic properties of the GB deviate only weakly from those of the bulk and are rather insensitive towards compressive and tensile strains. Our results thus indicate that experimentally observed piezotronic properties of wz bicrystals are not an intrinsic property of the pristine GB itself, but originate, for example, from externally supplied trapped charges, defects, impurities, or dopants. Low-energy structure models identified here may also be transferable to other wz- or zb-type IDBs (e.g., GaN, AlN, SiC, etc.).

中文翻译：

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原始纤锌矿ZnO {0001}反型畴边界的热力学稳定性和电子结构

最近，证实了含锌的纤锌矿（wz）ZnO双晶样品的电导率。 $\left\{0001\right\}$反转域边界（IDB）可以通过机械载荷进行大规模且可逆的调整。为了对此效果进行详细的微观了解，我们使用密度泛函理论计算系统地研究了此类IDB的原子结构和化学组成。总共构造，优化和热力学比较了结构和/或化学成分不同的92个模型几何。wz ZnO缺乏较高的对称性，因此无法直接计算单个晶界（GB）的多余能量。但是，我们证明，在wz的非周期性平板模型中$\left\{0001\right\}$对于IDB，附加的表面对总能量的贡献可以通过相应的闪锌矿（zb）表面的近似值来估算；后者可以通过一系列棱镜计算获得。减去这些表面能可让我们为wz IDB构造绝对GB能量图，并将其热力学稳定性与文献中已知的其他GB进行比较。我们发现热力学上受欢迎的IDBs具有完全（4倍）配位原子的特征，并且具有相对较低的过剩能量，范围从45到$95\mathrm{病毒}/{\mathrm{一个}}^2$，取决于IDB的端接（Zn / Zn或O / O）和计算中使用的交换相关函数（LDA，GGA或 $\text{GGA}+ü$）。GB的电子性能仅略微偏离整体，并且对压缩应变和拉伸应变不敏感。因此，我们的结果表明，实验观察到的wz双晶的压电性质不是原始GB本身的固有性质，而是例如源自外部提供的俘获电荷，缺陷，杂质或掺杂剂。这里确定的低能结构模型也可以转移到其他wz或zb型IDB（例如GaN，AlN，SiC等）。