  The influence of interactions in a reservoir coupled to a level on the width
of the filling as a function of the chemical potential and the position of the
level is studied. The density matrix renormalization group (DMRG) method is
used to calculate the ground state of a finite-size interacting reservoir,
linked to a single state dot. The influence of the interactions in the lead as
well as dot-lead interactions is considered. It is found that interactions in
the reservoir result in a decrease in the resonance width, while the dot-lead
interaction has an opposite effect. These effects are explained within the
random phase approximation as an effective change in the inverse
compressibility of the reservoir, while the dot-lead interactions renormalize
the position of the level.
