The dimeric nature of bonding in gallium: from small clusters to the α-gallium phase

Abstract

We consider the structural similarity of small gallium clusters to the bulk structure of α-gallium, which has been previously described as a molecular metal, via density functional theory-based computations. Previous calculations have shown that the tetramer, the hexamer, and the octamer of gallium are all structurally similar to the α-phase. We perform an analysis of the bonding in these clusters in terms of the molecular orbitals and atoms in molecules description in order to assess whether we can see similarities at these sizes to the bonding pattern, which is ascribed to the co-existence of covalent and metallic bonding in the bulk. The singlet Ga4 and Ga8 clusters can be constructed in a singlet ground state from the Ga-dimers in the first excited triplet state of the Ga2-molecule, the (3)Σg(-) state. Molecular orbital (MO) analysis confirms that the dimer is an essential building block of these small clusters. Comparison of the AIM characteristics of the bonds within the clusters to the bonds in the bulk α-phase supports the identification of the covalent bond in the bulk as related to the (3)Σg(-) state of the dimer.

Cluster melting: new, limiting, and liminal phenomena

“…120 GPa), after passing through several other phases, gallium does eventually adopt the same FCC structure as aluminium [72]. Intriguingly, experimental investigations suggest that the standard phase of gallium clusters is not known at all in the submicron regime (below approximately 0.8 µm) [73,74] (with of course the previously mentioned exception of the smallest molecular sizes [71]). …”

“…This structure manifests itself in the anisotropy of various properties of gallium, including conductivity [69,70]. Very small clusters of gallium are known to adopt this dimeric structure, but it is lost at sizes around 10 atoms where the structures become more similar to those of aluminium [71], before reappearing in the bulk. Under very high pressures (ca.…”

“…In this case, the usual criteria -a rapid increase in the Lindemann parameter, the onset of mobility of individual atoms, and a peak in the heat capacity -are shown to describe what remains essentially a melting transition down to the size of nine atoms. For eight atoms and smaller sizes, it is more realistic to think of these clusters as molecules: a remaining question however is how general this conclusion is, given that small gallium clusters of these sizes exhibit the molecular character of the bulk [71]. The answer is certainly hinted at by the observation that the transition from eight to nine atoms corresponds in gallium clusters to the size at which an internal atom is first possible, and this may be a more general predictor of the transition from molecule to cluster in different systems, where it may occur at different sizes.…”

Controllable Sliding Transfer of Wafer‐Size Graphene

“…As a result, the metallic bonds of Ga are not strong enough to ensure the atoms to form perfect crystal structures with close packing, for which the big radius of Ga atoms also contribute a lot. Accordingly, the bonding between the two nearest neighbors is more likely covalent 18, 19. Once melted, the imperfect crystal structures will be broken down and the bonds are loosened.…”

Bonding in doped gallium nanoclusters: Insights from regional DFT

“…Tonner and Gaston also note that in the 3 Σ g − excited triplet state, the 2σ g + orbital is empty and now both of the π u -orbitals are singly occupied. This leads to a formal bond order of one with only π-character but the electrons are more delocalized than in a typical π-bond [18]. Tonner and Gaston also recently investigated a number of small clusters and compared these with the structure of α-gallium [18].…”