Study On Vibration Spectrum Of Ice And Surface Adsorption Theory Of Water Molecules

Water ice are very common substances in our daily life,and the research in this field is a still hot topic.The hydrogen bonds play an important role in the study of water ice.Using first principles density functional theory,we focus on the particular role of hydrogen bond in the thermal dynamics and surface adsorption properties of water ice in this work.Firstly,using the CASTEP code of Material Studio(MS)platform,we investigated the vibrational spectrum of the ice Ⅱ.On the basis of good agreement with the experimental data of inelastic neutron scattering(INS),infrared(IR)absorption and Raman scattering spectroscopies,we analyze the normal modes from the intermolecular translation band,intermolecular libration band,intramolecular bending band and intramolecular stretching band.In the translation band,we confirm that two kinds of vibrational modes,named "four-bond vibration" and "two-bond vibration",constitute three main peaks ranging from 117 to 318 cm1.We also found that the cluster vibrational modes exist at lower frequencies,possibly overlapping with acoustic phonons.In the study of ice XV,Whale et al.found that there was a special mode that only one O-H bond stretching,while the other O-H bond keep static in the intramolecular stretching band.This phenomenon is common in this study,and we attribute it to the deformation of the localized tetrahedral structure.The technical route of comparing the simulated normal mode with the experimental spectrum enables us to assign the vibrational peaks scientifically.Secondly,in the study of ice Ⅴ,we identified a strategy to analyze the vibration modes of hydrogen disordered ice Ⅴ by comparing with ice ⅩⅢ.We calculated its phonon density of states,IR and Raman spectra focusing on the analysis of the vibrational modes of hydrogen bonds in the terahertz region.For the "four-bond vibration" vibrational mode,the molecule in the lattice vibrates against the surrounding four water molecules,while for the " two-bond vibration",the molecule vibrates along the two linked hydrogen bonds.In theoretically,the vibrational energy ratio of these two kinds of mode is approximately(?).It is worth mention that the distributions of these two kinds of modes overlap.We found that this is related to its broader distribution of bond lengths and bond angles.Its unique four-ring structure leads to the differentiation of bond angles.This feature is also found in its corresponding hydrogen-ordered ice ⅩⅢ.In addition,we constructed a model and simulated the adsorption behavior of water molecules on the NaCl surface using the least common divisor method.The results show that the water monomer is almost lay flat on the NaCl(001)surface,where one of the O-H bonds slopes slightly downward.This is quite different from the STM observations.In fact,the experimental observations are influenced by the Au(111)substrate,with the water molecules lay in the upright plane.However,the water tetramer forms a stable square structure on the surface,which is consistent with the experimental observations.The simulations show that the intermolecular hydrogen bonding is stronger than that of surface adsorption.