Lithium clusters Li-n (n = 1-20) have been investigated with density functional theory (DFT) and coupled-cluster (CC) methods. The global minima are located via an improved basin-hopping algorithm. Simulated polarizabilities are in good agreement with the measured data generally. The simulated polarizabilities for Li-6, Li-12 and Li-19 are in reasonable agreement when thermal effects are included, except the Li-3 cluster. A linear correlation for the inverse relationship between the CCSD calculated polarizabilities and ionization potential (IP) has been reported to have the linear coefficient of 0.996, which further strengthens our simulations. (C) 2015 Published by Elsevier B.V.