Recursive computation of matrix elements in the numerical renormalization group

Thenumerical renormalization group is an efficientmethod to diagonalizemodelHamiltonians describing correlated orbitals coupled to conduction states. While only the resulting eigenvalues are needed to calculate the thermodynamical properties for such models, matrix elements of Fermi operators must be evaluated before excitation and transport properties can be computed. The traditional procedure to calculatematrix elements is typically as expensive as the diagonalization of themodel Hamiltonian. Here, we present a substantially faster alternative that demands much less memory, yields equally accurate matrix elements and is easier to code. © 2014 Elsevier B.V. All rights reserved.