Huang Hong-Jui, Seenithurai Sonai, Chai Jeng-Da
Department of Physics, National Taiwan University, Taipei 10617, Taiwan.
Center for Theoretical Physics and Center for Quantum Science and Engineering, National Taiwan University, Taipei 10617, Taiwan.
Nanomaterials (Basel). 2020 Jun 25;10(6):1236. doi: 10.3390/nano10061236.
At the nanoscale, it has been rather troublesome to properly explore the properties associated with electronic systems exhibiting a radical nature using traditional electronic structure methods. Graphene nanoflakes, which are graphene nanostructures of different shapes and sizes, are typical examples. Recently, TAO-DFT (i.e., thermally-assisted-occupation density functional theory) has been formulated to tackle such challenging problems. As a result, we adopt TAO-DFT to explore the electronic properties associated with diamond-shaped graphene nanoflakes with = 2-15 benzenoid rings fused together at each side, designated as -pyrenes (as they could be expanded from pyrene). For all the values considered, -pyrenes are ground-state singlets. With increasing the size of -pyrene, the singlet-triplet energy gap, vertical ionization potential, and fundamental gap monotonically decrease, while the vertical electron affinity and symmetrized von Neumann entropy (which is a quantitative measure of radical nature) monotonically increase. When increases, there is a smooth transition from the nonradical character of the smaller -pyrenes to the increasing polyradical nature of the larger -pyrenes. Furthermore, the latter is shown to be related to the increasing concentration of active orbitals on the zigzag edges of the larger -pyrenes.
在纳米尺度上，使用传统电子结构方法来恰当地探索与具有自由基性质的电子系统相关的性质一直相当棘手。石墨烯纳米片是不同形状和尺寸的石墨烯纳米结构，就是典型的例子。最近，热辅助占据密度泛函理论（TAO-DFT）已被提出以解决此类具有挑战性的问题。因此，我们采用TAO-DFT来探索与菱形石墨烯纳米片相关的电子性质，这些纳米片在每一侧由2至15个苯环稠合在一起，被指定为-并四苯（因为它们可从并四苯扩展而来）。对于所考虑的所有值，-并四苯都是基态单重态。随着-并四苯尺寸的增加，单重态-三重态能隙、垂直电离势和基本能隙单调减小，而垂直电子亲和势和对称化的冯·诺依曼熵（这是自由基性质的一种定量度量）单调增加。当增加时，存在从较小-并四苯的非自由基特征到较大-并四苯不断增加的多自由基性质的平滑转变。此外，后者被证明与较大-并四苯锯齿边缘上活性轨道浓度的增加有关。
