The basis set used for the calculations in this section is def2-SVP. energy and generally yields reliable predictions for relative energies with an error ranging from 1 to 3 kcal/mol, which is at the same order order of magnitude of the DMET correlation energy error compared to the all electron result. In contrast, IAO+PAO partitioning not only recovers less correlation energy but also produces incorrect relative energies in several cases. Although the trend is qualitatively correct for isomers containing 7 water molecules, the relative energy is significantly lower than that reported using Löwdin partitioning and the all-electron results. A reason behind this is that as is mentioned above, Löwdin partitioning gives more delocalised orbitals that allows more inter-fragment interaction to be recovered. In addition, it is expected that the agreement between the all electron and the DMET result will be improved if a lower bath orbital truncation threshold ϵ is used. To demonstrate this, we perform the calculation on the 6-water and 7-water isomer using a smaller bath orbital truncation thresholds, and the results are shown in Table . According to this table, it is clear to see that as the threshold of choosing the bath orbitals ϵ is tightened, the accuracy when compared to the all-electron result becomes better at a cost of the increased size of the fragment. We note that if the value of ϵ becomes zero, then all of the localized atomic orbitals will become bath orbitals and the result will be exact. ϵ is similar to T PNO in a DLPNO-CCSD(T) calculation.