**1. Introduction**

Nanotubes (NTs) are prominent structures in many applications. From water desalination to microelectronics, their areas of application are wide. Their application areas are even getting broad every day, as they hold a promising future due to their distinctive properties. The discovery of carbon nanotubes (CNTs) by Sumio Iijima [1] has revolutionized the nano world. Since its discovery, the field of nanotechnology has achieved greater heights. Rubio et al. [2] predicted boron nitride nanotubes (BNNTs) in 1994, and they were experimentally discovered in 1995, by Chopra et al. [3]. In 2001, Hummer et al. [4] found that water can pass through CNTs spontaneously, using molecular dynamics simulation. Since then, many studies were carried out, using perfect CNTs and BNNTs for water transport and desalination. But the studies carried out on the deformed nanotubes are limited. Different types of deformation occur in nanotubes. They could be twisted, compressed, elongated, or bent during application and manufacturing. They could also have defects such as Stone–Wales, point vacancies, interstitials, etc., during manufacturing. He et al. [5] studied the effects of deformation degree and about the location of deformation in the carbon nanotubes on water transport. Feng et al. [6] showed that the transport diffusion of helium gas through deformed carbon nanotubes with screw deformation did not have any effect, while the XY-distortion and Z-distortion showed that the effect on transport diffusion is significant with an increase in temperature and distortions values. Even though there were earlier studies carried out on the water transport phenomena through deformed carbon nanotubes, water transport through nanotubes that have a twist or XY-distortion and Z-distortion have

not been studied extensively yet. Therefore, in this work, we studied the effect of deformations such as screw distortion, XY-distortion, and Z-distortion on water transport through long CNTs and BNNTs.

The effect of deformation on water transport through nanotubes is also of grea<sup>t</sup> importance to many biological, ion-selective channels. The ionic conduction through single-walled carbon nanotubes can directly be compared to them. Ion-channels are formed from proteins [7]. CNT-based nanodevices with controllable functions are widely used to mimic transmembrane channels. These transmembrane channels can be used as substitutes for certain channel proteins. Model membranes are needed to examine their application as transmembrane channels. Two methods are widely used to simulate this bio-membrane system [8]. The first method is to embed the CNT as channel in-between graphite sheets as the membrane. The atoms are deleted at desired locations, in order to accommodate the tube [9–11]. The second method is the CNT-bundle system. In this method, packed CNTs serve both as channels and the membrane to separate the reservoirs [12,13]. In this study, we used the first method. This study about the effect of deformation can be of greater use for designing transmembrane channels.
