Thermodynamics of Na_8 and Na_{20} clusters studied with ab-initio electronic structure methods

We study the thermodynamics of Na_8 and Na_{20} clusters using multiple-histogram methods and an ab initio treatment of the valence electrons within density functional theory. We consider the influence of various electron kinetic-energy functionals and pseudopotentials on the canonical ionic specific heats. The results for all models we consider show qualitative similarities, but also significant temperature shifts from model to model of peaks and other features in the specific-heat curves. The use of phenomenological pseudopotentials shifts the melting peak substantially (~ 50--100 K) when compared to ab-initio results. It is argued that the choice of a good pseudopotential and use of better electronic kinetic-energy functionals has the potential for performing large time scale and large sized thermodynamical simulations on clusters.Comment: LaTeX file and EPS figures. 24 pages, 13 figures. Submitted to Phys. Rev.

Density-based molecular dynamics study of melting in a finite-sized cluster: Al<SUB>13</SUB>

Ab initio molecular dynamical simulations have been performed to investigate the phenomenon of melting in a finite-size system, namely an Al13 cluster. Classical molecular dynamical simulations using Lennard-Jones potentials have shown that a coexistence region, where both solid-like and liquid-like behaviour is observed, exists over a range of total energy. Our density functional simulations on a metallic cluster aim at probing this coexistence region. Although our statistics is somewhat limited, we do find definite signatures of a coexistence region