Characterization of water structure in carbon nanotubes by various order parameters

Abstract

Various order parameters have been suggested to characterize the local structure of liquid water in bulk. Characterization the local structure of water molecules in the confined systems by various order parameters is important but still unclear. In this work, a series of popular order parameters are used to analyze the local structure of water molecules in carbon nanotubes (CNTs) by molecular dynamics simulation. Based on the value of order parameters, the different structures of water molecules in CNTs and in bulk were discussed. The orientational tetrahedral order (q) and translational tetrahedral order (Sk) are much better than local structure index (LSI) to describe the local structure of water in CNTs. We also demonstrated that the local structure of water molecules in the CNT(40,40) is almost the same with that in bulk. The findings could give us a guideline to investigate the water molecules in confined system.