We have carried out extensive isokinetic ab initio molecular-dynamic simulations to investigate the finite temperature properties of the impurity doped cluster Li6Sn and the host cluster Li-7. The data obtained from about 20 temperatures and total simulation time of at least 3 ns is used to extract thermodynamical quantities like canonical specific heat. We observe that, first, Li6Sn becomes liquidlike around 250 K, at much lower temperature than that for Li-7 (approximate to425 K). Second, a weak shoulder around 50 K in the specific heat curve of Li6Sn is observed due to the weakening of Li-Li bonds. The peak in the specific heat of Li-7 is very broad and the specific heat curve does not show any premelting features. (C) 2003 American Institute of Physics.