Hi there!
The memory needed for a computation with MCTDH-B for the coefficients is (N+M-1 over N)*(16 bytes [double precision complex])*(Dimension of Krylov subspace used for the integrator). The size of the Krylov subspace is adaptive, i.e., it depends on the particular problem studied; but it can be controlled using the "Minimal_Krylov" and "Maximal_Krylov" inputs in the MCTDHX.inp file.
In addition, M*N_g*[O(10)]*(16 bytes [double precision complex]) of memory is needed for the solution of the orbital equation.
Regards,
Axel