Departament de Ciència de Materials i Química Física and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, E-08028 Barcelona, Spain.
Departament de Ciència de Materials i Química Física and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, E-08028 Barcelona, Spain and SorbonneUniversités, UPMC Univ Paris 06, CNRS, Laboratoire de Chimie Théorique CC 137, 4, place Jussieu F. 75252, Paris Cedex 05, France.
Nanoscale. 2017 Jan 19;9(3):1049-1058. doi: 10.1039/c6nr05788h.
Bottom-up and top-down derived nanoparticle structures refined by accurate ab initio calculations are used to investigate the size dependent emergence of crystallinity in titania from the monomer upwards. Global optimisation and data mining are used to provide a series of (TiO) global minima candidates in the range N = 1-38, where our approach provides many new low energy structures for N > 10. A range of nanocrystal cuts from the anatase crystal structure are also considered up to a size of over 250 atoms. All nanocrystals considered are predicted to be metastable with respect to non-crystalline nanoclusters, which has implications with respect to the limitations of the cluster approach to modelling large titania nanosystems. Extrapolating both data sets using a generalised expansion of a top-down derived energy expression for nanoparticles, we obtain an estimate of the non-crystalline to crystalline crossover size for titania. Our results compare well with the available experimental results and imply that anatase-like crystallinity emerges in titania nanoparticles of approximately 2-3 nm diameter.
自下而上和自上而下衍生的纳米颗粒结构经过精确的从头计算进行了优化，用于研究从单体向上的 TiO2 中结晶度随尺寸的变化。全局优化和数据挖掘提供了一系列 N = 1-38 范围内的 (TiO) 全局最小候选物，我们的方法为 N > 10 提供了许多新的低能量结构。还考虑了锐钛矿晶体结构的一系列纳米晶体切割，尺寸超过 250 个原子。考虑到的所有纳米晶体相对于非晶纳米团簇都是亚稳态的，这对使用团簇方法对大型 TiO2 纳米系统进行建模的局限性有影响。使用自上而下衍生的纳米颗粒能量表达式的广义扩展对两个数据集进行外推，我们得到了 TiO2 的非晶到结晶转变尺寸的估计值。我们的结果与现有的实验结果很好地吻合，表明在大约 2-3nm 直径的 TiO2 纳米颗粒中出现了类似锐钛矿的结晶度。
