Molecular Dynamics Investigation Of The Medium Range Order In Supercooled Water

In this paper, medium-range structure of water in supercooled region have been investigated by molecular dynamics simulation. The method of medium-range structure representation of water in supercooled region and medium-range structure of water in supercooled region at different densities are also discussed.We use molecular dynamics simulation to investigate medium-range structure of water in supercooled region. Besides the prepeak at about Q¹.86 （?）^-1 in the oxygen-oxygen partial structure factor observed previously, a characteristic peak of 30°in second coordination shell angle distribution is first found which indicates fine medium-range structure. We have succeeded to explain these results by introducing a corner-sharing tetrahedra （CST） model. This model can help to understand the fundamental nature of water.Using molecular dynamics simulation, we present a detailed structural analysis of short and medium range order of supercooled water. At 0.9, 1.0 and 1.1 g/cm³, the tetrahedral arrangement of hydrogen bond is gradually constructed by oxygen atoms with decreasing temperature. As a consequence, there appears obvious CST structure at medium-range order. It shows fine medium range structure. At 1.2 and 1.3 g/cm³, the characteristic peak of 30°in second coordination shell angle distribution is less obvious. It indicates that the structure varies from LDA with obvious CST structure before 1.1 g/cm³ to HDA and VHDA with less obvious CST structure after that. This structure transition with density is non-linear, which abruptly occurs at 1.1 g/cm³.In summary, the medium range structure of supercooled liquid water is studied by molecular dynamics simulations, which provides some basis to understand the essence of glass transition in future.