Molecular dynamics study of the structural formation of short chain molecules: Structure and molecular mobility

By carrying out molecular dynamics simulations of 100 short chain molecules, each of which consists of 20 CH2 groups, we show that the orientationally ordered structure is formed at low temperature by a sudden cooling from a random configuration at high temperature. The essentially extended chains form a monolayer structure. The ratio of the lattice constants a/b takes the hexagonal value root 3 at 400 K and decreases as the temperature decreases. From detailed analysis of the local orientational order, it is found that the growth of the local ordered clusters proceeds in a stepwise fashion. From the analysis of the molecular mobility, we find that the longitudinal chain motion increases dramatically with increasing temperature while the transverse chain motion is not sensitive to the temperature variation.