Theoretical Study On Several Typical One-dimensional Confined Systems At Ambient And High Pressure Conditions

The typical one-dimensional （1-D） nanochannels of single-walled carbonnanotubes （SWCNTs） and AlPO₄-5（AFI） are the ideal models to study the1-Dconfined system, the encapsulated atoms or molecules in these1-D nano-materialscan exhibit a lot of fantastic properties, which different from the body materials. Thestudy on these hybrid materials not only can help us to understand the interactionmechanism of1-D confined system, but also can discover plenty of newphenomenons, new features and new physical laws. In this paper, the structure ofseveral1-D confined systems with SWCNT and AFI packing different molecules havebeen studied detailed at ambient and high pressure condition by theoreticalsimulation.The1-D nano-peapod, which forming by filling periodical C₆₀molecules intoSWCNT, has attracted great enthusiasm since its discovery. The molecular orientationand deviating position from the tube axis are the focus issues in the scientificcommunity. In this paper, we studied the influence of intermolecular interaction on thepreferable orientation of encapsulated C₆₀molecules into SWCNTs with differentchirality and diameter. We revealed the physical picture of molecular orientations forthe encapsulated C₆₀molecules in this work, and found the preferable orientation isirrelevant to the tube’s chirality, but dependents on the diameter. The results show thatthe C₆₀molecule exhibits the preferable pentagon and hexagon orientations for thesmall and large tubes, respectively. For the diameters increased from1.31to1.36nm,the preferable orientations of C₆₀molecule are relevant to the orientation ofneighboring C60molecule, which exhibit a alternant orientation. It is worthmentioning that we found a new vertex orientation. The results also show that thezigzag phase of encapsulated C₆₀molecules confined in SWCNTs has been foundwhen the diameter is larger than1.4nm, and the deviated distance from the tube axisis proportional to the tube diameter.We studied the preferable orientation, translation movement and stackingstructure of encapsulated C₆₀H_18molecules into SWCNTs with different chirality anddiameter by using the energy analysis and molecular dynamics simulation. The resultsshow that the preferable orientation of encapsulated C₆₀H₁8molecule is onlydependents on the tube diameter, for which change from the slanting states（intersection angle between C3Vaxis and tube axis decrease with increase the the tube diameter） into the parallel state with increasing the tube diameter. The studies alsoshow that the translation movement of C₆₀H₁₈molecule along the tube axis directionis restricted for the diameter smaller than1.45nm. For the diameter lager than1.57nm, the C₆₀H18molecule will deviate from the tube axis and various stacking phases,such as zigzag chain, thrple helix, double-molecule layer and4-helix phase, have beenfound with increasing the tube diameter.The FC@SWCNT（13,0） peapod structure, which is formed by encapsulating theferrocene molecules into the SWCNTs, has a wide range of application in variousprospects. At present, the study of this peapod structure is still staying in the ambientconditions, the study on the high pressure conditions are also in the primary stage. Inthis paper, the high pressure structure and properties of FC@SWCNT（13,0） have beenstudied in detailed by Density Functional Theory （DFT）. The results show that thelying ferrocene molecule happens to a slight torsion around the tube axis, and theencapsulated tube will translate into a oval shape with the pressure up to3GPa, andthe flat oval shape of tube has been found with the pressure up to8GPa, due to thesupporting role of encapsulated ferrocene molecules. And a crushed tube has beenobtained when the pressure reached to23GPa. In addition, we found the band gap ofFC@SWCNT（13,0） is decreased with increasing the pressure, which is closed withthe pressure up to9GPa.Iodine （I2） is the typical diatomic molecule, which can assemble into the longchain structure when encapsulated into the AFI channel, thus it is the ideal materialsto synthetic1-D quantum wires. The experimental studies show that the length of I2chain in the AFI channel can be increased by pressure, but a clear physical picture ofgrowth mechanism for the I2chain in AFI channel by pressure can’t be provide inexperiment. In this paper, we studied the preferable orientations and Raman vibrationin detailed by using the classical force field and Density Functional Theory （DFT）.The results show that the standing iodine molecules translate into the lying states withincreasing the pressure, which induced a longer I2chains. The Raman vivration oflying iodine molecules show a redshift with increasing the pressure, while a blueshifthas been observed for the standing iodine moelcules. We reveal that the mutation ofRaman vibration for the lying and standing iodine molecules at5GPa is due to theelliptical deformation of AFI channel. The above studies can not only help usunderstand the interaction mechanism of1-D confinement system, but also canexpand the application field of low dimensional nano-materials.