  We present an implementation of the hybridization expansion impurity solver
which employs sparse matrix exact-diagonalization techniques to compute the
time evolution of the local Hamiltonian. This method avoids computationally
expensive matrix-matrix multiplications and becomes advantageous over the
conventional implementation for models with 5 or more orbitals. In particular,
this method will allow the systematic investigation of 7-orbital systems
(lanthanide and actinide compounds) within single-site dynamical mean field
theory. We illustrate the power and usefulness of our approach with dynamical
mean field results for a 5-orbital model which captures some aspects of the
physics of the iron based superconductors.
