  There are three essential problems in computational relativistic chemistry:
electrons moving at relativistic speeds, close lying states and dynamical
correlation. Currently available quantum-chemical methods are capable of
solving systems with one or two of these issues. However, there is a
significant class of molecules, in which all the three effects are present.
These are the heavier transition metal compounds, lanthanides and actinides
with open d or f shells. For such systems, sufficiently accurate numerical
methods are not available, which hinders the application of theoretical
chemistry in this field. In this paper, we combine two numerical methods in
order to address this challenging class of molecules. These are the
relativistic versions of coupled cluster methods and density matrix
renormalization group (DMRG) method. To the best of our knowledge, this is the
first relativistic implementation of the coupled cluster method externally
corrected by DMRG. The method brings a significant reduction of computational
costs, as we demonstrate on the system of TlH, AsH and SbH.
