Ionic versus metallic bonding in AlnNam and AlnMgm (m ≤ 3, n + m ≤ 15) clusters

Abstract

First principles electronic structure studies on the ground state geometries, stability, and the electronic structure of AlNa and AlMg (m ≤ 3, n + m ≤ 15) clusters have been carried out to examine the nature of bonding between Na or Mg and Al. Identifying whether the bonding is ionic or metallic in bulk materials is typically straightforward; however, in small clusters where quantum confinement is important, the nature of bonding may become unclear. We have performed a critical analysis of the bonding in these bimetallic clusters using charge analysis, electrical dipole moments, hybridization of the atomic orbitals, the Laplacian of the charge density at the bond critical points, and the change in the bonding energy between neutral and anionic forms of the cluster. For NaAl clusters, we find that the Na binding is primarily ionic, while the bonding in AlMg is primarily metallic. We find that the Mulliken population of the 3p orbital of Na and Mg can provide a rapid assessment of the nature of bonding. We also find that the Hirshfeld charge and dipole moments are effective indicators, when placed in context. We found that the Laplacian of the charge density at the bond critical points can be misleading in identifying whether the bonding is ionic or metallic in small clusters.

Enhanced Zintl anions by carbon doping in Al‐Na clusters and new magic structure Al6Na4C

“…In order to show the effect of carbon doping on the stabilities, we also include in Table the Al 6 Na 2 and Al 6 Na 4 clusters for comparison. The lowest‐energy structures of these two clusters were studied by using different methods . Al 6 Na 2 has 20 valence electrons and corresponds to a strong magic structure.…”

“…Cameron et al studied the geometries, stabilities, and the electronic structures of Al n Mg m and Al n Na m ( m ≤ 3, n + m ≤ 15) clusters and examined the bonding nature using DFT approaches. They also considered that the bonding between Na and Al n moieties is ionic . The above results show that the Al atoms with all of the valence electrons form (Al n ) q − Zintl anions in alkaline‐doped aluminum clusters because the Al 3+ cores attract the electrons much stronger than the alkaline metal cations AM + .…”

Density Functional Theory Modeling of Reactions of Addition of H2 Molecules to Magnesium Clusters Mg17M Doped with Atoms M of Transition 3d Elements

“…These studies were carried out at the molecular level using quantum-chemical (mostly, DFT) calculations in combination with mass spectrometry, X-ray photoelectron spectroscopy, and IR spectroscopy in inert matrices. To date, hydrides of the Mg m H n series ( m = 1–4 and n = 1–8), mixed magnesium–aluminum clusters Al n Mg m ( m ≤ 3, n + m ≤ 15), and their negative ions have been detected experimentally. − Their DFT calculations demonstrated that the most stable species are the “magic” clusters Al 5 Mg 2 – , Al 11 Mg 2 – , Al 7 Mg 3 – , and Al 11 Mg 3 – . Systematic DFT studies performed for a wider family of mixed Mg 28– n Al n clusters ( n = 0–28), Mg 55‑ n Al n ( n = 0–55), and homonuclear Mg n isomers ( n = 2–56) − ,, have demonstrated that the enthalpies of Mg/Al mixing are negative for all components.…”

Massive dipoles across the metal–semiconductor cluster interface: towards chemically controlled rectification

“…In this work, we have chosen the MgAl 12 cluster with 38 valence electrons for the metal-based component. 37,38 The cluster needs two electrons to acquire a filled shell and is marked by a significant electron affinity enabling it to act as a strong acceptor. Noting this valence state, we chose Re 6 Se 8 (PMe 3 ) 5 for the semiconductor-based cluster as the previous work 39 has shown that a Re 6 Se 8 cluster marked by covalent bonds is highly stable at +2 charge-state.…”