Ab initio studies of quasi-one-dimensional pentagon and hexagon ice nanotubes

Abstract

Ab initio plane-wave total-energy calcuation is carried out to study the relative stability of the quasi-one-dimensional (Q1D) pentagon and hexagon ice nanotubes. Electronic structure calculations indicate the two Q1D ice nanotubes have nearly the same band structures and energy bandgap as those of proton-ordered bulk ice Ih. Ab initio molecular-orbital and density-functional theory calculations, as well as three classical potential models of water, are also employed to investigate the relative stability of the pentagon and hexagon water clusters (H2O)30, (H2O)60, and (H2O)120. Clusters of this kind can serve to bridge the gap between the small polygonal water rings and the infinitely long Q1D polygon ice nanotubes. It is found that the polygon water prisms with the size (H2O)120 begin to show the relative energetic behavior of the infinitely long polygon ice nanotubes.

Fingerprints in IR OH vibrational spectra of H2O clusters from different H-bond conformations by means of quantum-chemical computations

“…[1,9] Thus many studies have been presented on the structure of water clusters from small to large sizes both experimentally and theoretically. [10][11][12][13][14][15][16][17][18][19][20] For small clusters with up to ten water molecules, most computational ab initio investigations predict approximately the same geometries, which are consistent with experimental results. [1,2,4,7,10,14] However, for a large cluster, it is still a challenge to obtain the structure that corresponds to the global minimum energy since the conformational space grows exponentially as the size of cluster increases.…”

Ferroelectric Ordering in Ice Nanotubes Confined in Carbon Nanotubes

“…Some relaxed structures of the ice nanotubes and the polarized directions are both shown in Fig.1. These results consistent with those of Koga et al [13,14,15,16]. As illustrated in Fig.1, the ice nanotubes have 4, 5, and 7 side faces corresponding to inside (14,0), (15,0), and (17,0) SWCNTs, respectively.…”

“…Recent investigations have increased our understanding of confined water, showing that, in nanoscopic proportions, many water properties differ drastically from those of bulk water [10,11,12]. In particular, an excellent model is water confined in carbon nanotubes, which have been adopted in many previous studies [13,14,15,16,17,18,19,20,21,22,23,24,25,26]. Among these interesting investigations, Koga et al investigated water inside single-walled carbon nanotubes (SWCNTs) of diameter 1.1∼1.4 nm and found that water forms ice nanotubes composed by a rolled square ice sheet [14,15,16].…”

“…In particular, an excellent model is water confined in carbon nanotubes, which have been adopted in many previous studies [13,14,15,16,17,18,19,20,21,22,23,24,25,26]. Among these interesting investigations, Koga et al investigated water inside single-walled carbon nanotubes (SWCNTs) of diameter 1.1∼1.4 nm and found that water forms ice nanotubes composed by a rolled square ice sheet [14,15,16]. Recent neutron scattering studies, combined with molecular dynamics (MD) simulations, revealed that water in SWCNTs of diameter 1.4 nm forms a core-shell structure, in which the square ice sheet described by Koga et al is coupled with a chainlike configuration at the center of the shell [27,28].…”

“…We chose a high axial-pressure (P zz =200MPa) condition and four types of zigzag SWCNTs, which are (14,0), (15,0), (16,0), and (17,0) with diameters of 10.96Å, 11.74Å, 12.53Å, and 13.31Å, respectively. During our MD simulations, the temperature was lowered stepwise staring from 450K to 100K and then heated stepwise back.…”