Aguilera-Del-Toro R H, Aguilera-Granja F, Balbás L C, Vega A
Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, E-47011 Valladolid, Spain.
Instituto de Física, Universidad Autónoma de San Luis Potosí, 78000 San Luis Potosí, Mexico.
Phys Chem Chem Phys. 2017 Jan 25;19(4):3366-3383. doi: 10.1039/c6cp06225c.
We report a comprehensive theoretical study of the structural and electronic properties of neutral and charged nickel oxide clusters, NiO (n = 3-8 and m = 1-10), in the context of recent experiments of photodissociation and Ion Mobility Mass Spectrometry. By means of density functional theory calculations in the generalized gradient approximation for exchange and correlation, we determined the putative ground states as well as the low-energy structural- and spin-isomers which were then used to explore the favorable fragmentation channels of the nickel oxide cationic clusters, and the resulting most abundant products, in good qualitative agreement with photodissociation measurements. Apart from stoichiometries different from those of their nickel oxide macroscopic counterparts, we found a tendency to form compact Ni subclusters, with reentrance of low-coordinated structures close to the equiatomic Ni-O concentration, taking the form of alternating Ni-O rings in the smaller sizes, in good qualitative agreement with Ion Mobility Mass Spectrometry measurements. This structural pattern is manifested in a drop of the total spin magnetic moment close to the equiatomic concentration due to the formation of antiparallel magnetic couplings. Although antiparallel couplings are found to a more or less extent in most clusters, especially in the oxygen rich phase, we identified certain clusters of special interest in the context of magnetic grains because of their large total magnetic moment and abundance. There are even some nickel oxide clusters with a higher total moment than their pure Ni counterparts, due to parallel magnetic couplings and the contribution of the oxygen atoms to the total moment.
结合最近的光解离和离子迁移质谱实验，我们对中性和带电氧化镍团簇NiO（n = 3 - 8且m = 1 - 10）的结构和电子性质进行了全面的理论研究。通过采用广义梯度近似的密度泛函理论计算来处理交换和关联，我们确定了假定的基态以及低能量结构异构体和自旋异构体，进而用于探索氧化镍阳离子团簇的有利碎片化通道以及由此产生的最丰富产物，所得结果与光解离测量结果在定性上吻合良好。除了化学计量比与其宏观氧化镍对应物不同外，我们发现存在形成紧凑镍亚团簇的趋势，在接近等原子镍 - 氧浓度时低配位结构再次出现，在较小尺寸下呈现交替镍 - 氧环的形式，这与离子迁移质谱测量结果在定性上吻合良好。由于反平行磁耦合的形成，这种结构模式在接近等原子浓度时总自旋磁矩下降中得以体现。尽管在大多数团簇中或多或少都发现了反平行耦合，尤其是在富氧相中，但鉴于其较大的总磁矩和丰度，我们在磁性颗粒的背景下确定了某些特别有趣的团簇。甚至有一些氧化镍团簇的总磁矩比其纯镍对应物更高，这归因于平行磁耦合以及氧原子对总磁矩的贡献。
