Equation of motion approach to the solution of the Anderson model

Based on an equation of motion approach the single-impurity Anderson model is reexamined. Using the cluster expansions the equations of motion of Green functions are transformed into the corresponding equations of motion of connected Green functions, which provides a natural and uniform truncation scheme. A factor of 2 missing in the Lacroix's approximation for the Kondo temperature is gained in the next higher-order truncation beyond Lacroix's. A quantitative improvement in the density of states at the Fermi level is also obtained.