How a single aluminum atom makes a difference to gallium: First-principles simulations of bimetallic cluster melting

First principles molecular dynamics simulations of Ga19Al(+) have been performed in the microcanonical ensemble using parallel tempering. We perform a thorough investigation of the changes induced by the presence of an Al atom in the Ga dominated cluster. Dynamic analysis indicates that the Al atom prefers to occupy the internal sites of the cluster structure, at all temperatures, and above 450 K, the Al atom is less mobile than the central Ga atom throughout the simulation. Using the multiple histogram method, canonical specific heat curves are obtained that compare well with previous experimental measurements of the specific heat and equivalent simulations for the Ga20 (+) cluster. The first-principles melting temperature agrees well with the experimental value for Ga19Al(+). Analysis of the root mean squared fluctuation in bond length, velocity auto-correlation function, and the corresponding power spectrum, confirms the solid-liquid-like phase transition in Ga19Al(+), as for Ga20 (+).