Method to include explicit correlations into density-functional calculations based on density-matrix functional theory

A variational formulation for the calculation of interacting fermion systems based on the density-matrix functional theory is presented. Our formalism provides for a natural integration of explicit many-particle effects into standard density-functional-theory-based calculations and it avoids the ambiguities of double-counting terms inherent in other approaches. Like the dynamical mean-field theory, we employ a local approximation for explicit correlations. Aiming at the ground state only, we trade some of the complexity of Green's-function-based many-particle methods against efficiency. Using short Hubbard chains as test systems, we demonstrate that the method captures ground-state properties, such as left-right correlation, beyond those accessible by mean-field theories.