Melting temperatures and negative specific heat in Na clusters .
Heat capacities of NaN N= 13, 20, 55, 135, 142 and 147 clusters have been investigated using a many body Gupta potential and microcanonical molecular-dynamics simulations. Negative heat capacities around the cluster meltinglike transition have been obtained for N= 135, 142, and 147, but the smaller clusters (N= 13,20, and 55) do not show this peculiarity. By performing a survey of the cluster potential-energy lanscape (PEL) it is found that the width of the distribution function of the kinetic energy and the spread of the distribution of potential-energy minima (isomers) are useful features to determine the different behavior of the heat capacity as a function of the cluster size. The effect of the range of the interatomic forces is studied by comparing the heat capacities of the Na55 and Cs55 clusters.
"Negative heat capacity of sodium clusters"
Juan A. Reyes-Nava, Ignacio L.Garzón, and, Karo Michaelian
Physical Review B 67, 2003, 1654014.
Comparison of the maximum values of Z(2) E(black dots for the NaN cluster. The upper insets shows tha maximum value of the Z(2) E for the Cd55 cluster. The upper insets show the energy dependene of the caloric curve and the heat capacity of the Cd55 cluster. The inset at the low right corner shows the gE as a function of the normalized mean deviation of the kinetic energy of the Cd55 cluster, and its comparison with Na55, calculated at E=4.37eV and E=2.71 eV respectively.
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