Pawluk Tiffany, Hirata Yasuhiro, Wang Lichang
Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, IL 62901, USA.
J Phys Chem B. 2005 Nov 10;109(44):20817-23. doi: 10.1021/jp053563b.
The energetics and the electronic and magnetic properties of iridium nanoparticles in the range of 2-64 atoms were investigated using density functional theory calculations. A variety of different geometric configurations were studied, including planar, three-dimensional, nanowire, and single-walled nanotube. The binding energy per atom increases with size and dimensionality from 2.53 eV/atom for the iridium dimer to 6.09 eV/atom for the 64-atom cluster. The most stable geometry is planar until four atoms are reached and three-dimensional thereafter. The simple cubic structure is the most stable geometric building block until a strikingly large 48-atom cluster, when the most stable geometry transitions to face-centered cubic, as found in the bulk metal. The strong preference for cubic structure among small clusters demonstrates their rigidity. This result indicates that iridium nanoparticles intrinsically do not favor the coalescence process. Nanowires formed from linear atomic chains of up to 4-atom rings were studied, and the wires formed from 4-atom rings were extremely stable. Single-walled nanotubes were also studied. These nanotubes were formed by stacking 5- and 6-atom rings to form a tube. The ring stacking with each atom directly above the previous atom is more stable than if the alternate rings are rotated.
利用密度泛函理论计算研究了含2 - 64个原子的铱纳米颗粒的能量学、电子和磁性性质。研究了多种不同的几何构型，包括平面、三维、纳米线和单壁纳米管。每个原子的结合能随着尺寸和维度的增加而增大，从铱二聚体的2.53 eV/原子增加到64原子团簇的6.09 eV/原子。最稳定的几何构型在达到四个原子之前是平面的，之后是三维的。直到一个显著大的48原子团簇之前，简单立方结构是最稳定的几何构建单元，当达到该团簇时，最稳定的几何构型转变为面心立方，这与体相金属中的情况相同。小团簇对立方结构的强烈偏好表明了它们的刚性。这一结果表明铱纳米颗粒本质上不倾向于聚结过程。研究了由多达4原子环的线性原子链形成的纳米线，由4原子环形成的纳米线极其稳定。还研究了单壁纳米管。这些纳米管是通过堆叠5原子环和6原子环形成的。每个原子直接位于前一个原子上方的环堆叠比交替环旋转的情况更稳定。
