Fragment molecular orbital method: analytical energy gradients

The fragment molecular orbital (FMO) method, which aimed to calculate large molecules such as proteins, was proposed in a previous work. The method divides a molecule into small fragments and performs MO calculations on the fragments and the fragment pairs to obtain the total energy of molecule. The method with the analytical energy gradient at the HF level of theory has been incorporated into the Gaussian 94 (G94) package. Geometry optimization calculations using the energy gradients were successfully performed on a model peptide, methyl-capped glycine trimer.