Measuring the photoluminescence of defects in crystals is a common experimental technique for analysis and identification. However, current theoretical simulations typically require the simulation of a large number of atoms to eliminate finite size effects, which discourages computationally expensive excited state methods. We show how to extract the room-temperature photoluminescence spectra of defect centres in bulk from an $\mathrm{\textit{ab-initio}}$ simulation of a defect in small clusters. The finite size effect of small clusters manifests as strong coupling to low frequency vibrational modes. We find that removing vibrations below a cutoff frequency determined by constrained optimization returns the main features of the solid state photoluminescence spectrum. This strategy is illustrated for an NV$^{-}$ defect in diamond, presenting a connection between defects in solid state and clusters; the first vibrationally resolved $\mathrm{\textit{ab-initio}}$ photoluminescence spectrum of an NV$^{-}$ defect in a nanodiamond; and an alternative technique for simulating photoluminescence for solid state defects utilizing more accurate excited state methods.
Effect of photonic crystal stop-band on photoluminescence of $a$-Si$_{1-x}$C$_x$:H
分析了由\textit{a} C $_x$：H和\textit{a}非晶层交替构成的一维（1D）光子晶体的周期结构中光子态局域密度变化的影响.使用\textit{a} -Si $_{1-x}$ C $_x$：H作为发射材料使得可以检查光致发光光谱轮廓的变换，其在宽度上与光子阻带相当。实验表明，在阻带附近，发光被增强和抑制。在阻带不同边缘的发光峰的相对强度随单个\textit{a} -Si $_{1-x}$ C $_x$：H薄膜的阻带位置和光致发光峰的失谐而变化。在所考虑的系统中的Purcell效应的理论描述的方法，其中的局域光子态密度的计算方面的一维模型。%实验测量和计算光谱之间获得了良好的一致性。结果表明，局域态密度的特定部分在1D光子晶体的阻带的长波长（低频）边缘处显著增加，这是由于光波的电场在\textit{a} -Si $_{1-x}$ C $_x$：H的空间区域中的主要局域化，该空间区域与\textit{a} -SiO $_2$相比具有更高的相对介电常数。
Semiempirical pseudopotential approach for nitride-based nanostructures and {\it ab initio} based passivation of free surfaces
本文提出了一种基于屏蔽原子赝势和\textit{ab initio}计算的半经验赝势方法。这种方法的动机是对能够解决纳米结构的赝势的需求，其中\textit{ab initio}方法在局部密度近似的水平上既太昂贵又不够准确，而介观有效质量方法由于沿着至少一个维度的结构的小尺寸而不适用。在这项工作中，我们改进了传统的赝势方法，通过两个步骤的过程：首先，我们反演了一组自洽确定的屏蔽{ \it ab initio}势在纤锌矿GAN的一系列晶胞体积，从而确定球对称和结构平均的原子势。其次，我们调整的潜力，以重现观察到的激发能。我们发现，调整代表了一个合理的小扰动的潜力，使随后的潜力仍然再现原来的波函数，而激发能显着改善。此外，我们处理的自由表面的悬挂键的钝化，这是相关的纳米线和胶体纳米粒子的研究。我们提出了一种方法，从{ \it ab initio}计算得到钝化赝势。我们应用我们的赝势方法的GAN纳米线的电子结构上的限制效应的探索。
Insights into the need for ab-initio calculations to accurately predict the optical properties of metallic carbon nanotubes based on experimental confrontation
