Fragment molecular orbital-based molecular dynamics (FMO-MD) method with MP2 gradient

► A droplet model consisting of 64 water molecules was simulated by the fragment molecular orbital-based molecular dynamics (FMO-MD) method with the 6-31G∗ basis set, in order to evaluate the oxygen-oxygen radial distribution function (RDF). ► The first peak position was thus determined as 2.75 Å at the second-order Møller-Plesset perturbation level with three-body FMO correction (or FMO3-MP2). ► This estimate was in agreement with an X-ray value of 2.73 Å, whereas the corresponding Hartree-Fock (FMO3-HF) value was as long as 2.89 Å. ► The importance of electron correlation effect was just demonstrated.