Energy Consideration of Molecular Layer Stacking in n-Alkane Crystal

Abstract

The details of the molecular layer stacking in the low-temperature ordered (LO) phases of n-alkane with an odd carbon number were investigated by calculating the layer stacking energy.In order to express the layer stacking, a parameter Δ b is defined as the relative shift of the upper layer to the lower layer along the b-axis.The layer stackings with two specific positive and negative Δ b values (Δ b=+b_p, -b_n) have minimum energy. In phases I and V, the energy at the positive Δ b is lower than that at the negative Δ b; the layer stacking with positive Δ bis considered to be more stable. While in phase IV, the energies at both shifts Δ b areequal; the stabilities of the two stackings are the same.The values of relative shift with the minimum energies in each LO phaseapproximately correspond to those values determined using X-ray diffraction.