Structures and ionization energies of small lithium doped germanium clusters

Abstract

We present a combined theoretical and experimental investigation of neutral and cationic lithium doped germanium clusters, Ge_nLi_m (n = 5–10; m = 1–4). The vertical ionization energies and ionization thresholds are derived from threshold photoionization efficiency curves in the 4.68–6.24 eV range and are compared with calculated vertical and adiabatic ionization energies for the lowest energy isomers obtained using DFT computations. The agreement between experimental and computed values supports the identification of the ground state structures. Charge population analysis shows that lithium transfers its valence electron to the Ge_n hosts to form Ge_n^mδ−–mLi^δ+ and Ge_n^(mδ−+1)–mLi^δ+ complexes. This is also illustrated by the strong correlation between the size dependent lithium adsorption energies in Ge_nLi and the Ge_n electron affinities. Neutral Ge_nLi_m clusters are formed by adsorbing lithium atoms on either triangular or rhombic faces of the Ge_n framework with the lithium atoms tending to avoid each other. The chemical bonding phenomena of clusters are analyzed in detail using the densities of states and molecular orbitals.