Electronic effects on the melting of small gallium clusters

Motivated by experimental reports of higher-than-bulk melting temperatures in small gallium clusters, we perform first-principles molecular dynamics simulations of Ga20 and Ga 20+ using parallel tempering in the microcanonical ensemble. The respective specific heat (CV) curves, obtained using the multiple histogram method, exhibit a broad peak centered at approximately 740 and 610 K—well above the melting temperature of bulk gallium (303 K) and in reasonable agreement with experimental data for Ga 20+. Assessment of atomic mobility confirms the transition from solid-like to liquid-like states near the CV peak temperature. Parallel tempering molecular dynamics simulations yield low-energy isomers that are ∼0.1 eV lower in energy than previously reported ground state structures, indicative of an energy landscape with multiple, competing low-energy morphologies. Electronic structure analysis shows no evidence of covalent bonding, yet both the neutral and charged clusters exhibit greater-than-bulk melting tem...