Orbital-free molecular dynamics study of melting in K20, K55, K92, K142, Rb55, and Cs55 clusters -: art. no. 115404

The meltinglike transition in potassium clusters K-N, with N=20, 55, 92, and 142, is studied by using an orbital-free density-functional constant-energy molecular dynamics simulation method, and compared to previous theoretical results on the meltinglike transition in sodium clusters of the same sizes. Melting in potassium and sodium clusters proceeds in a similar way: a surface melting stage develops upon heating, before the homogeneous melting temperature is reached. Premelting effects are nevertheless more important and more easily established in potassium clusters, and the transition regions spread over temperature intervals which are wider than in the case of sodium. For all sizes considered, the percentage of melting temperature reduction when passing from Na to K clusters is substantially larger than in the bulk. Once those two materials have been compared for a number of different cluster sizes, we study the meltinglike transition in Rb-55 and Cs-55 clusters, and make a comparison with the melting behavior of Na-55 and K-55. As the atomic number increases, the height of the specific-heat peaks decreases, their width increases, and the melting temperature decreases as in bulk melting, but in a more pronounced way.