Atomic layering and related postmelting effects in small liquid metal clusters

Abstract

The specific heat of Na_25, as obtained by first-principles molecular dynamics simulations, shows interesting anomalies above the melting phase-change region: a) It steadily decreases with increasing temperature, an effect observed also in bulk liquid metals. This trend is explained in terms of the gradual conversion of vibrational modes into diffusion modes; b) on top of this decreasing trend, the specific heat shows broad undulations, induced by the temperature-dependent atomic layering in the liquid cluster. Extended liquid metal surfaces also show atomic layering, but it does not affect the bulk heat capacity. This effect is therefore genuine of finite atomic systems and should be expected to be quite general in metal clusters.