  In order to better understand Kondo insulators, we have studied both the
symmetric and asymmetric Anderson lattices at half-filling in one dimension
using the density matrix formulation of the numerical renormalization group. We
have calculated the charge gap, spin gap and quasiparticle gap as a function of
the repulsive interaction U using open boundary conditions for lattices as
large as 24 sites. We find that the charge gap is larger than the spin gap for
all U for both the symmetric and asymmetric cases. RKKY interactions are
evident in the f-spin-f-spin correlation functions at large U in the symmetric
case, but are suppressed in the asymmetric case as the f-level approaches the
Fermi energy. This suppression can also be seen in the staggered susceptibility
and it is consistent with neutron scattering measurements in CeNiSn.
