Finally, to examine the ability of applying BE-i-FCIQMC in calculating realistic systems, two organic molecules, namely benzene and cyclohexane, are chosen, and the level of theories are BE1-FCIQMC/6-31G* and BE1-i-FCIQMC/6-31G, respectively. As the sizes of the Hilbert space for the fragments are 1.40 × 10 15 and 7.31 × 10 12 , they are too large for any deterministic FCI solvers to be implemented. BE1-i-FCIQMC calculations are done for each of the compound, and the recovered correlation energies are then compared with deterministic BE1-CCSD, BE2-CCSD, BE3-CCSD, as well as all-electron CCSD and CCSD(T) using the same basis set. The results are shown in Figures and, in which all the correlation energy values are compared with the all-electron CCSD(T) correlation energy. It can be shown from the graphs that even if the type of Bootstrap Embedding is 1, which is technically equivalent to Density Matrix Embedding since there are no overlapping fragments, and each fragment only contains one carbon atom and its connected hydrogen atom(s), BE1-i-FCIQMC is already capable of recovering the correlation at all-electron CCSD level in benzene and allelectron CCSD(T) level in cyclohexane. These observations clearly demonstrate the potential of applying BE-i-FCIQMC in realistic molecules.