We perform hybrid density functional calculation to study the energetics, electronic properties, optical transitions, and migration barriers of native defects in CaWO$_4$. Oxygen and calcium vacancies are most likely to form in the absence of doping, but interstitials could also incorporate. Tungsten-related defects are unlikely to be present. The positively charged $V_{\rm O}$ and the negatively charged $V_{\rm Ca}$ are likely to form complexes. Calculated optical transition levels indicate that experimentally observed absorption and emission peaks can be attributed mainly to oxygen-related defects. Calculations of migration barriers allow us to conclude that Ca$_i^{2+}$, $V_{\rm O}^{2+}$ and O$_i^{2-}$ are highly mobile, even below room temperature. We have also examined Er dopants, finding that erbium easily substitutes on the Ca site in a positive charge state. Erbium can form complexes with $V_{\rm Ca}$ and O$_i$, which would deactivate the Er. If Er is introduced by implantation, Er interstitials are likely present, which will produce emission that is prone to spectral diffusion and blinking. Our calculated properties of Er$_i$ explain why annealing at modest temperatures allows the interstitials to move into substitutional sites and point defects to move away, resulting in stable emission.
The role of native defects in the transport of charge and mass and the decomposition of Li$_{4}$BN$_{3}$H$_{10}$
Li $_{4}$ BN $_{3}$ H $_{10}$分别由于其高氢含量和高锂离子电导率而对于氢储存和锂离子电池固体电解质具有极大的兴趣。然而，由于在分解过程中氨（NH $_{3}$）的不可逆性和共生，这种复合氢化物的实际储氢应用受到限制。我们报告的第一性原理密度泛函理论研究的本地点缺陷和缺陷复合物在Li $_{4}$ BN $_{3}$ H $_{10}$，并提出了一个原子机制的材料的分解，涉及质量输运介导的本地缺陷。鉴于这种特定的机制，我们认为，NH $_{3}$的释放与材料内部带负电荷的氢空位的形成和迁移有关，并且可以通过掺入合适的电活性杂质来操纵。我们还发现Li $_{4}$ BN $_{3}$ H $_{10}$容易在Li亚晶格上产生Frenkel无序;锂空位和杂质是高度可移动的，在质量传输和离子传导中起着重要作用。
