  We compute the magnetic susceptibility and specific heat of the spin-1/2
Heisenberg model on the kagome lattice with high-temperature expansions and
exact diagonalizations. We compare the results with the experimental data on
ZnCu3(OH)6Cl2 obtained by Helton et al. [Phys. Rev. Lett. 98, 107204 (2007)].
Down to k_BT/J~0.2, our calculations reproduce accurately the experimental
susceptibility, with an exchange interaction J~190K and a contribution of 3.7%
of weakly interacting impurity spins. The comparison between our calculations
of the specific heat and the experiments indicate that the low-temperature
entropy (below ~20K) is smaller in ZnCu3(OH)6Cl2 than in the kagome Heisenberg
model, a likely signature of other interactions in the system.
