Kondo effect in a quantum dot-the atomic approach

We describe the Kondo resonance in quantum dots employing the atomic approach for the Anderson impurity. The starting point of this approach is the exact solution of the Anderson impurity in the zero-bandwidth limit, and we choose the level of the atomic conduction band so that the completeness relation be satisfied. There are two or more solutions close to the chemical potential that satisfy this condition at low temperatures, and we choose the one with minimum Helmholtz free energy, considering that this corresponds to the Kondo solution. At low temperatures we obtain a density of states that characterizes well the structure of the Kondo peak. The results obtained for both the localized density of states at the chemical potential and for dynamical properties (like the conductance) agree very well with those obtained by the numerical renormalization group formalism and by the slave boson mean field approach, respectively. This result is a consequence of the satisfaction of the Friedel sum rule by the atomic approach in the Kondo limit. As a simple application we calculate the conductance of a side-coupled quantum dot