  We combine density-functional theory with density-matrix functional theory to
get the best of both worlds. This is achieved by range separation of the
electronic interaction which permits to rigorously combine a short-range
density functional with a long-range density-matrix functional. The short-range
density functional is approximated by the short-range version of the
Perdew-Burke-Ernzerhof functional (srPBE). The long-range density-matrix
functional is approximated by the long-range version of the Buijse-Baerends
functional (lrBB). The obtained srPBE+lrBB method accurately describes both
static and dynamic electron correlation at a computational cost similar to that
of standard density-functional approximations. This is shown for the
dissociation curves of the H$_{2}$, LiH, BH and HF molecules.
