Many-body expansion (MBE) has been carried out to investigate two- to five-body energy terms and their contributions to the interaction energy (IE) of (H₂O)₁₅ cluster. We have observed that the erroneous contribution of many-body terms on IE originated from cheaper convergence thresholds set as default in popular quantum mechanics packages. The propagation of errors from smaller to higher-body terms, due to the combinatorial nature of MBE, is also observed.
