Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ, UK.
Nanoscale. 2011 Sep 1;3(9):3780-7. doi: 10.1039/c1nr10486a. Epub 2011 Aug 9.
We calculate the optical absorption spectra of low-energy uncapped zinc sulfide nanostructures found by global optimisation (basin-hopping/simulated annealing) using time-dependent density functional theory (TD-DFT) and compare the results with experimental spectra. We predict that for all nanostructures studied the lowest excited state found by TD-DFT corresponds to an exciton with an exciton binding energy that is much larger than that of excitons in bulk zinc sulfide. We further show that for the more symmetrical nanostructures some of the excitons are dark and that the absorption on-sets, the energy of the lowest exciton, for the different nanostructures show no clear evidence of quantum confinement. We propose that this apparent lack of quantum confinement finds its origin in the fact that the lowest exciton is not evenly spread over the whole nanostructure but shows large contributions for specific groups of atoms. Finally, we show that the predicted optical absorption spectra fit with those reported experimentally.
我们使用含时密度泛函理论（TD-DFT）计算了通过全局优化（盆地跳跃/模拟退火）找到的低能无帽硫化锌纳米结构的光吸收谱，并将结果与实验谱进行了比较。我们预测，对于所有研究的纳米结构，TD-DFT 发现的最低激发态对应于激子，其激子结合能远大于体相硫化锌中的激子。我们进一步表明，对于更对称的纳米结构，一些激子是暗激子，并且不同纳米结构的吸收起始能，即最低激子的能量，没有明显的量子限制证据。我们提出，这种明显缺乏量子限制的现象源于这样一个事实，即最低激子不是均匀分布在整个纳米结构上，而是在特定的原子群中表现出较大的贡献。最后，我们表明，预测的光吸收谱与实验报道的谱相吻合。
