document: For any quantum dynamical method, existing or emerging, reliable benchmarks are required to assess their accuracy. A model Hamiltonian exhibiting tunnelling dynamics through a multidimensional asymmetric double well potential has been used as a test by the MP/SOFT [18] and CCS methods [19] mentioned above, and also more recently by a configuration interaction (CI) expansion method [20] and two-layer version of CCS (2L-CCS). [21] The Hamiltonian consists of a 1-dimensional tunnelling mode coupled to an (M−1)-dimensional harmonic bath, hence it is a system-bath problem which bears some similarity to the Caldeira-Leggett model of tunnelling in a dissipative system [22,23]. This Hamiltonian is non-dissipative, however and the harmonic modes all have the same frequency. System-bath models play an important role in physics, being used to describe superconductivity at a Josephson junction in a superconducting quantum interface device (SQUID) [24], for which the Caldeira-Leggett model provides a theoretical basis, and magnetic and conductance phenomena in the spin-bath regime [25].