We study the thermodynamics of ${\mathrm{Na}}_8$ and ${\mathrm{Na}}_{20}$ 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 $(\sim 50–100\hspace{0.5em}\mathrm{K})$ when compared to ab initioresults. 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-size thermodynamical simulations on clusters.

• Received 26 November 2000

DOI:https://doi.org/10.1103/PhysRevB.64.045408