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

Ab initio pseudopotential total-energy calculation was performed to affirm the existence of polymorphs of quasi-one-dimensional (Q1D) ice nanotube. It was found that both hexagon and pentagon ice nanotubes are metastable solid phases in vacuum at 0 K and they are nearly isoenergetic. Furthermore, calculation of the electron density of states indicated that the two Q1D polymorphs have nearly the same energy bandgap as the proton-ordered bulk ice. Finally, the relative stability of the finite-size pentagon and hexagon water clusters at 0 K was also characterized using all-electron quantum chemistry methods as well as three additional classical potential models of water.