Theoretical Study of the Structure and Stability of Layerwise Hydrogenated Aluminum Clusters Al44Hn and Al89Hm

摘要

Structural parameters, energies, and spectroscopic characteristics of two series of layerwise hydrogenated aluminum clusters Al44Hn (n = 27-44) and Al89Hm (m = 15, 24, 39, and 63) have been calculated by the density functional theory method. It has been shown that increasing number of H atoms in both series entails rapid enhancement of structural distortions up to cooperative rearrangements accompanied by a change in the shape and composition of the surface layer and internal core of the cluster. At the end of the first series Al44Hn, several surface atoms migrate to the outer sphere of the cage to form valence-unsaturated outer-surface AlHn and Al2Hn moieties, which can be active sites at the stages of deeper hydrogenation. Simultaneously, the inner core [Al](5) disintegrates, and its atoms are introduced into the surface layer. A family of inverted Al42H42 isomers with the hollow [Al-42] cage has been localized; the isomers contain the endohedral AlH4 group and inner Al-H bonds with their hydrogen end directed to the center of the inner cavity. At the end of the second series, five alanate groups AlH4 and two Al3H2 fragments bonded to the surface through hydrogen bridges are formed in the outer sphere of the Al89H63- cluster. The results are of interest for DFT modeling of hydrogenation of nanosized aluminum clusters at the molecular level.