Polarization and Structure of Small Clusters

TL;DR

This study explores how the structure of the Li4Ge4 cluster varies with charge transfer and polarizability, revealing multiple stable geometries and instability conditions, and discusses implications for similar alkali-tetralide clusters.

Contribution

It provides a detailed phase diagram of Li4Ge4 structures as functions of charge transfer and polarizability, highlighting new stable and unstable configurations.

Findings

Cubic structure at low charge transfer (Q<0.5)

Multiple stable geometries at higher charge transfer and polarizability

Instability occurs when Ge polarizability induces dipoles larger than Ge diameter

Abstract

In this paper we report the structure of the Li4Ge4 cluster as a function of charge transfer and polarizability. We find that for small charge transfer (Q < 0.5) this cluster has the expected cubic structure: a Ge4 tetrahedron with a Li ion attached at large distance to each face. With increasing charge transfer Q > 0.5 the structure of Li4Ge4 changes: for relative small polarizability of the Ge ion the Ge4 breaks up into two Ge2 pairs separated by the four Li. For larger polarizability there are three possibilities: 1) for full charge transfer the Li ions break up the Ge subcluster into four separated ions; 2) for smaller values of the charge transfer we still have the structure with two Ge2 pairs and 3) for intermediate values of, charge transfer the Ge sublattice forms a structure with two opposite bonds of the Ge4 tetrahedron cluster broken. These are the only stable geometries found. For large Ge polarizability we find that all structures become unstable: the size of the induced dipole moment becomes larger than the diameter of Ge. Based on this phase diagram of Li4Ge4 we discuss the structure of other A4M4 alkali(= A)--tetralide (= M) (= group 14) clusters, and related solid state structures