Molecular dynamics study of the structures and dynamics of the iodine molecules confined in AlPO(4)-11 crystals.

Structural and dynamical properties of iodine molecules incorporated in one-dimensional elliptic channels of AlPO(4)-11 (AEL) crystals were studied by means of molecular dynamics (MD) simulations. It was found that the iodine molecules in the AEL channels are restricted in the (101) planes with only two favorite orientations: lying along the channels and standing along the major axes of the ellipses, which are well consistent with the experimental observations. In addition, the iodine structures are largely dependent on the loading level: with the increase of loading, the iodine specimens change their structures accordingly from isolated molecules as in the gas phase to single molecular chains and molecular ribbon sheets. The molecular ribbon sheets are composed of equally distributed and parallel molecules as in the iodine crystals. The simulation results show that the standing iodine molecules in the AEL channels are well restricted due to both the appropriate size of ellipses and their alternation throughout the channels. They can diffuse along the channels only after overcoming the rotational barriers to become lying molecules, which indicate that the iodine molecules in the ribbon sheets can keep the configurations without rotational and translational motion. The confined iodine molecules with such structures and properties may be used to improve the accuracy of the frequency standards.