Comparison of two-quantum-cluster approximations
نویسندگان
چکیده
We provide microscopic diagrammatic derivations of the molecular coherent potential approximation ~MCA! and dynamical cluster approximation ~DCA! and show that both are F derivable. The MCA ~DCA! maps the lattice onto a self-consistently embedded cluster with open ~periodic! boundary conditions, and therefore violates ~preserves! the translational symmetry of the original lattice. As a consequence of the boundary conditions, the MCA ~DCA! converges slowly ~quickly! with corrections O(1/Lc) @O(1/Lc)# , where Lc is the linear size of the cluster. These analytical results are demonstrated numerically for the onedimensional symmetric Falicov-Kimball model.
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