MD simulations of confined water and silicon were carried out to investigate liquid to solid phase transition phenomena in the confinement system. The simulations provide possible evidence of new low-dimensional polymorphs of silicon and ice. The low-dimensional structures were further examined by using ab initio methods. Two five-site potential models of water were employed to study liquid to quasitwo-dimensional solid transitions of water. The simulations of five-site models confirm our previous simulation results on basis of the four-site TIP4P model of water. Ab initio plane-wave total-energy calculation 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. Atomistic computer simulation evidences are also presented for possible existence of low dimensional silicon structures. The local geometric structure of low dimensional structures are different from the local tetrahedral structure of cubic diamond silicon even though the coordination number of atoms of the low-dimensional silicon allotropes is still four-fold. Ab initio calculations show that the low-dimensional silicon structures are locally stable in vacuum and have zero bandgap, suggesting that they are possibly metals rather than wide-gap semiconductors
