  Density matrix embedding theory (DMET) [Phys. Rev. Lett.2012, 109, 186404]
has been demonstrated as an efficient wave-function-based embedding method to
treat extended systems. Despite its success in many quantum lattice models, the
extension of DMET to real chemical systems has been tested only on selected
cases. Herein, we introduce the use of the complete active space
self-consistent field (CASSCF) method as a correlated impurity solver for DMET,
leading to a method called CAS-DMET. We test its performance in describing the
dissociation of a H-H single bond in a H10 ring model system and an N=N double
bond in azomethane (CH3-N=N-CH3) and pentyldiazene (CH3(CH2)4-N=NH). We find
that the performance of CAS-DMET is comparable to CASSCF with different active
space choices when single-embedding DMET corresponding to only one embedding
problem for the system is used. When multiple embedding problems are used for
the system, the CAS-DMET is in a good agreement with CASSCF for the geometries
around the equilibrium, but not in equal agreement at bond dissociation.
