Condensation and phase transition of hydrogen molecules confined in single-walled carbon nanotubes

The condensation and phase transitions of hydrogen molecules confined in single-walled carbon nanotubes have been studied using ab initio calculations and molecular dynamics simulations. At low temperature the van der Waals surface of a narrow (5,5) tube forces the H₂ molecules to form quasi-one-dimensional lattices with the H₂ molecular orientation highly polarizing along the axial direction of the tube. Various H₂ lattice structures are observed in (5,5) and (10,10) tubes when the density of H₂ molecules is changed. At higher temperature clear solid-liquid phase transitions are observed.