Collect. Czech. Chem. Commun. 2007, 72, 278-295

Quantum Effects on the Caloric Curves of Lithium Clusters

Fernand Spiegelman* and Florent Calvo

Laboratoire de Chimie et Physique Quantiques, UMR5626 du CNRS, IRSAMC, Université Paul Sabatier, 118 Route de Narbonne, F-31062 Toulouse Cedex, France


A tight-binding quantum Hamiltonian and an empirical embedded-atom model (EAM) potential are used to get insight into the finite-temperature behavior of small Lin clusters, n = 8, 20, and 55. Exchange Monte Carlo simulations provide an extensive sampling of configuration space, including the putative global minimum and many relevant isomers. The heat capacities obtained from the classical simulations are corrected for low-temperature quantum delocalization using the Pitzer-Gwinn approximation. Alternatively, the caloric curves are estimated from the database of local minima using the quantum harmonic superposition approximation. While the two atomistic models predict qualitatively similar features, including some premelting effects in Li20 but none in Li55, strong variations are observed in the melting temperatures, the EAM potential giving unexpectedly low values.

Keywords: Caloric curves; Lithium clusters; Tight-binding; Embedded atom model; Monte Carlo simulations; Heat capacity.

References: 86 live references.