Local density of states subject to finite impurity concentration in   graphene
  It is demonstrated that there is a characteristic impurity concentration, at which variation with concentration and overall appearance of the local density of states at the impurity site in graphene are changing their behavior. Features that are prominent in the local density of states for the single impurity are disappearing from it when impurity concentration far exceeds this critical value. The impurity subsystem not only induces the rearrangement of the electron spectrum in graphene, but also undergoes a substantial spectral transformation by itself, which can be observed experimentally. 
Yuriy V. Skrypnyk and Vadim M. Loktev