Paper title:
Structure of water confined inside carbon nanotubes and water models

Journal:
Materials Chemistry and Physics 132 (2012) 682? 687

Author/s:
Yoshimichi Nakamura (a,*), Takahisa Ohno (b)
(a) Computational Materials Science Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
(b) JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan

Summary: 
In this paper, the effect of n-site water models on molecular dynamics (MD) simulations of water structures inside carbon nanotubes (CNTs) open to a water reservoir at ordinary ambient conditions was studied. Specifically, the accuracy of three water models was compared: 3-, 4- and 5-site models.

Three-site water models include TIP3P and SPC/E in which the molecular charge distribution is modeled by point charges on the nuclei. A 4-site water model such as TIP4P differs from a 3-site model because it places the negative charge on an additional fictive site. Five-site models, such as TIP5P and TIP5P-E, consider negative charges along the lone-pair directions. Hence, they reproduce water properties more realistically and accurately but they have higher computational requirements.

Density distribution along the radial direction and the net axial polarization of water inside (8,8) and (9,9) CNTs were determined and were concluded to be model dependent.

Confined water modeled using TIP3P was found to have a less ordered structure compared to the other models. The structure for SPC/E and TIP4P water models resembled a stacked column of water layers. TIP5P-E water model was able to produce ferroelectric mobile water.


Contribution and application:
To effectively model desalination on a molecular level, it is important to understand the principles behind water models so a proper decision may be made in choosing which water model best suit the system. Further study about water structure in different types of nanotubes may also be made based on this paper.



By: Hannah Ebro
hannah@gist.ac.kr