The three-body fragment molecular orbital method for accurate calculations of large systems

The approximations used in the context of the fragment molecular orbital method were critically revised, the origin of the approximation error determined and an improvement proposed. The three-body method which has been so far very expensive, was reformulated to be used with the approximations, and its efficacy both in terms of accuracy and computational timings carefully established on a set of representative systems. Timings and accuracy are reported for the two and three-body methods, including their application to two proteins 1L2Y and 1IO5 (PDB codes) and (H2O)1024 (at the RHF/6-31G∗ level).