Dipole Moment, Hydrogen Bonding and IR Spectrum of Confined Water

Abstract

Drastic changes can take place in the structure, dynamics, and thermodynamics of a fluid when it is confined to spaces of molecular dimensions, as compared to its bulk counterpart. Water confinement in the nanometer-scale channels and pores of inorganic open framework materials, such as zeolites, are of great scientific interest. Zeolites are crystalline aluminosilicates, with various controlled pore sizes and connectivities. [1] From a practical point of view, water plays a key role in many applications, includingion-exchang e and separation. From a more general point of view the interaction of water with solid surfaces is of key importance for many chemical and physical processes. However, our present understandingof interfacial or confined water at the molecular level is still very limited. Most of the experimental techniques are difficult to carry out in nanometer environments. Theoretical investigation is, thus, a great help for a better understanding of confined water properties. Classical simulations have recently been performed aimed at understandingthe structure, dynamics, and thermodynamics of water confined in carbon micropores or nanotubes [2, 3] and zeolites. [4–8] However, the quantum nature of bondingin water can only be captured by ab initio calculations. Elaborate treatments of the electronic density are usually limited to small clusters (or a few adsorbed molecules) and restricted to equilibrium structures. The Car–Parrinello molecular dynamics method (CPMD) [9] offers an alternative route to capture the electronic properties of molecules, as well as dynamical effects. Such DFT-based ab initio molecular dynamics calculations have been already applied to bulk water, [10] interfacial water on Si surfaces, [11] and zeolitic materials. [12, 13] Most of the CPMD stud