First-principles study on the infrared spectra of ice nanotubes

The structures and infrared (IR) spectra of ice nanotubes (INTs) are studied by the density functional theory and density functional perturbation theory in the generalized gradient approximation. Applying the group theory, we analyze the vibrational properties of the IR-active modes in the connectivity, librational, bending, intra-ring OH stretching, and inter-ring OH stretching regions. The origins of the IR-active modes are systematically investigated. Our calculation shows that the unusual form of hydrogen bonds in the INTs plays an important role in the signatures of their IR spectra, especially in the inter-ring OH stretching region, whose frequencies are significantly higher than those in ice-Ih case; Our result is in good agreement with an available experimental and theoretical report.