Plessow Philipp N
Institute of Catalysis Research and Technology (IKFT), Karlsruher Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Phys Chem Chem Phys. 2020 Jun 21;22(23):12939-12945. doi: 10.1039/d0cp01651a. Epub 2020 Jun 1.
The rearrangement of transition metal nanoparticles from cuboctahedral to icosahedral structures is studied for up to 923 atoms. The atomic structure and temperature dependence of the transition are investigated with a well-defined collective variable. This collective variable describes the folding of the square fcc(100) facets into two triangular facets through a linear combination of the diagonals of all fcc(100) facets of all shells of the particle. Activation barriers are determined through harmonic transition state theory and constrained molecular dynamics simulations based on force field potentials. These calculations predict an activation entropy larger than 1 meV K, leading to strongly temperature dependent activation barriers. Density functional theory calculations were additionally performed both as single point calculations and as full optimizations. Cu, Ag, Au and Ni clusters show low barriers for concerted, symmetric transition up to the 309-atomic clusters. In contrast, for Pd, Pt, Rh and Ir higher barriers are required, already for the 147-atomic clusters. With increasing barriers, an asymmetric but still concerted rearrangement becomes energetically more favorable than the fully symmetric transformation. The material-dependence of the transition can be correlated with the melting point of the bulk metals.
研究了多达923个原子的过渡金属纳米颗粒从立方八面体结构到二十面体结构的重排。利用一个定义明确的集体变量研究了过渡的原子结构和温度依赖性。这个集体变量通过粒子所有壳层的所有面心立方（fcc）(100)面的对角线的线性组合来描述正方形fcc(100)面折叠成两个三角形面。通过谐波过渡态理论和基于力场势的约束分子动力学模拟确定活化能垒。这些计算预测活化熵大于1 meV K，导致活化能垒强烈依赖于温度。此外，还进行了密度泛函理论计算，包括单点计算和完全优化。对于铜、银、金和镍团簇，直到309原子团簇，协同对称转变的能垒都很低。相比之下，对于钯、铂、铑和铱，即使是147原子团簇，也需要更高的能垒。随着能垒的增加，不对称但仍协同的重排比完全对称的转变在能量上更有利。转变的材料依赖性可以与块状金属的熔点相关联。
