For the calculation with 4, 8 and 25 degrees of freedom, the Smolyak scheme with the system-bath separation is used. The relation between, nb i λi and λ i are: (i) nb 1 λ1 = 1 + 36λ 1 ; (ii) nb 2 λ2 = 1 + 4λ 2 ; (iii) nb i λi = 1 + 2λ i for the bath modes. The same relations are used for nq i λi . The convergence of the properties will be checked against L s , the system Smolyak parameter. L b , the bath parameter, is fixed to 2, the coupling parameter, L m , is defined as L s + 1 and the Smolyak grib parameter, L G is L m + 1. In Table , we can see that the energy is already converged for L s = 6. However, L s = 7 is needed to converge the populations up to 200 fs with an accuracy of 0.1 %. Furthermore, it is worth noting that all properties remain almost unchanged when L b = 3 is used. For the 4D-model (n = 4), the comparison between the direct-product scheme and the Smolyak scheme shows an excellent agreement for the energy and the populations up to 200 fs. However, the computation with Smolyak scheme is about 30 time faster than the one with the direct-product approach. For a larger number of degrees of freedom, only calculations with the Smolayk scheme are possible in a reasonable time.