Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi 55, 20125 Milano, Italy.
J Chem Phys. 2017 Oct 28;147(16):164701. doi: 10.1063/1.4994165.
TiO nanoparticles (NPs) are nowadays considered fundamental building blocks for many technological applications. Morphology is found to play a key role with spherical NPs presenting higher binding properties and chemical activity. From the experimental point of view, the characterization of these nano-objects is extremely complex, opening a large room for computational investigations. In this work, TiO spherical NPs of different sizes (from 300 to 4000 atoms) have been studied with a two-scale computational approach. Global optimization to obtain stable and equilibrated nanospheres was performed with a self-consistent charge density functional tight-binding (SCC-DFTB) simulated annealing process, causing a considerable atomic rearrangement within the nanospheres. Those SCC-DFTB relaxed structures have been then optimized at the DFT(B3LYP) level of theory. We present a systematic and comparative SCC-DFTB vs DFT(B3LYP) study of the structural properties, with particular emphasis on the surface-to-bulk sites ratio, coordination distribution of surface sites, and surface energy. From the electronic point of view, we compare HOMO-LUMO and Kohn-Sham gaps, total and projected density of states. Overall, the comparisons between DFTB and hybrid density functional theory show that DFTB provides a rather accurate geometrical and electronic description of these nanospheres of realistic size (up to a diameter of 4.4 nm) at an extremely reduced computational cost. This opens for new challenges in simulations of very large systems and more extended molecular dynamics.
TiO 纳米粒子（NPs）如今被认为是许多技术应用的基本构建块。形态被发现起着关键作用，球形 NPs 具有更高的结合性能和化学活性。从实验的角度来看，这些纳米物体的特性非常复杂，为计算研究提供了广阔的空间。在这项工作中，我们使用两尺度计算方法研究了不同尺寸（300 至 4000 个原子）的 TiO 球形 NPs。使用自洽电荷密度泛函紧束缚（SCC-DFTB）模拟退火过程进行全局优化以获得稳定和平衡的纳米球，导致纳米球内发生相当大的原子重排。然后，使用 DFT（B3LYP）理论对那些 SCC-DFTB 弛豫结构进行优化。我们对结构特性进行了系统的和比较性的 SCC-DFTB 与 DFT（B3LYP）研究，特别强调了表面与体相的比例、表面位点的配位分布和表面能。从电子的角度来看，我们比较了 HOMO-LUMO 和 Kohn-Sham 隙、总态密度和投影态密度。总的来说，DFTB 与杂化密度泛函理论之间的比较表明，DFTB 以极低的计算成本，对这些实际尺寸（最大直径为 4.4nm）的纳米球提供了相当准确的几何和电子描述。这为更大系统的模拟和更广泛的分子动力学提出了新的挑战。
