Chemistry Department, Georgetown University, 37th and O Streets, NW, Washington, DC 20057-1227, USA.
Phys Chem Chem Phys. 2010 Nov 14;12(42):14017-22. doi: 10.1039/c0cp00523a. Epub 2010 Sep 21.
Point defects and pores in diamond affect its optical and electrical properties. We generated and evaluated a large number of vacancy V(n) clusters representing nanosized voids in diamonds for n up to 65. Our generational algorithm spawns the new generation n + 1 from the list of the most stable structures in the previous generation n. With energy as the only criterion, we generate a large structural diversity that allows their unbiased analysis. Since π-electron delocalization is important for carbon, we used quantum mechanical tight-binding density functional theory (TBDFT). Adamantane-like globular shapes are preferred for n up to ∼22. Beginning around n≈ 35, the most stable structures show overall oblate shapes with some irregularities. These novel structures have not been seen before because hitherto only highly regular structures were considered. We see local graphitization in these relaxed structures providing an atomistic justification for the widely used "slit pore" model. The preference for structures with minimum number of cut bonds diminishes as n increases. There are no particularly stable "magic" sizes for vacancy clusters larger than n = 22 indicating that these larger voids can easily incorporate small vacancies and vacancy clusters. Radial distribution analysis shows that unusual contact or bond distances in the 1.6 to 2.8 Å range appear in the vicinity of the internal surfaces of the vacancy clusters. Extremely long C-C bonds emerge as a result of structural relaxation of the dangling bonds in the vicinity of the vacancy clusters that cannot be simply described by ordinary sp(2)/sp(3) hybridization.
金刚石中的点缺陷和孔隙会影响其光学和电学性质。我们生成并评估了大量空位 V(n) 团簇，代表金刚石中的纳米级空隙，其中 n 最高可达 65。我们的生成算法从前一代 n 中最稳定结构的列表中生成新一代 n + 1。仅以能量作为标准，我们生成了大量的结构多样性，允许对其进行无偏分析。由于 π 电子离域对于碳很重要，因此我们使用了量子力学紧束缚密度泛函理论 (TBDFT)。对于 n 最高可达 ∼22 的情况，类金刚烷的球状形状是首选。大约从 n≈35 开始，最稳定的结构表现出整体扁球形，带有一些不规则性。这些新结构以前从未见过，因为迄今为止只考虑了高度规则的结构。我们在这些松弛结构中看到局部石墨化，为广泛使用的“狭缝孔”模型提供了原子合理性。随着 n 的增加，具有最小切割键数的结构的偏好性降低。对于大于 n=22 的空位团簇，没有特别稳定的“魔术”尺寸，这表明这些较大的空隙可以容易地包含小的空位和空位团簇。径向分布分析表明，在空位团簇内部表面附近的 1.6 到 2.8 Å 范围内会出现不寻常的接触或键距。由于在空位团簇附近的悬空键的结构弛豫，会出现非常长的 C-C 键，这不能简单地用普通的 sp(2)/sp(3) 杂化来描述。
