We begin by examining the impact of the sparsity threshold, ϵ, on the energy calculations. The DMET simulations are performed using the DMET code in-house, which is built on a modified version of the PySCF framework. The necessary integrals, including the 3-and 4-index, are generated using libcint. Unrelaxed 1-PDM and cumulant 2-PDM are employed for density matching and energy calculations, with the cutoff threshold for bath orbitals set at 10 -8 . The convergence threshold for the matching error is set to 1 × 10 -6 , leading to a small error of approximately 5 × 10 -5 E h . We first investigate how the threshold influences the accuracy of calculations on water-molecule clusters containing 10, 15, 20, 25, 30 and 35 water molecules. With respect to covalently bonded systems, although similar methodologies can be applied, the amount of correlation energy recovered would be much less than that of the all-electron result, since the interfragment interaction is much stronger. Attempts on covalent systems will therefore be left as a future work.