Different kinds of porous materials and molecular structures of representative gases in atmosphere are presented. The molecular potential pictures of atoms and molecules confined in graphitic slit micropores and cylindrical mesopores are given on the basis of Lennard-Jones potential. The quasi-high pressure effect, highly concentrated Xe cluster formation, ordered structure formation of water, and highly oriented structure of ethanol in graphitic micropores near ambient temperature are discussed in terms of molecular potential.
Zeolitic pores are known to be regular in terms of their shape as well as their size. Since their sizes are in the order of nano meter, the adsorbed molecules should experience the overlapping of adsorption potential field in the pores. Therefore, even adsorbed molecules due to weak van der Waals interaction behave specifically in zeolitic pores and exhibit rather large interaction energy. Pore size regularity results into the molecular sieve effect of zeolites, which causes peculiar catalytic behavior of zeolites. Zeolitic charge unbalance, which originates from the co-existence of metal atoms with different valences, is also the cause of specific adsorption and catalytic behavior. Adsorption behavior of molecules in/on zeolitic nano-scale pores as well as the nature of active adsorption sites of zeolitic surfaces is described. In particular, adsorption behavior is emphasized from the energetic point of view.
When alkali metals are loaded into nano-space of zeolite crystals, cationic clusters of alkali atoms are stabilized there. The s-electrons of alkali atoms are shared with many other alkali atoms in cages, and occupy quantum levels, such as 1s, 1p, etc. These s-electrons in clusters show novel properties depending on the structure of clusters, quantum mechanical effect on s-electrons, Coulomb interaction between s-electrons, degeneracy of 1p orbitals, spin-orbit interaction and also the intercluster interaction. In K-loaded K-form zeolite LTA, ferromagnetic properties are observed depending on the average loading density of guest K atoms, although no magnetic element is contained there. Metal-to-insulator transition occurs when alkali metal is changed from K to Na in zeolite FAU, where Na and K clusters are in Mott insulator and strongly correlated electrons, respectively. Observed electronic properties are closely related to the structural properties of alkali atoms in the zeolite regular cages, such as superstructures.
Liquid molecules take on a layered structure in the very vicinity of solid surface and effects of this structure on the tribological characteristics cannot be neglected when lubricant film thickness between solid surfaces is less than several times of the molecular diameter. The layered structure of liquid molecules is due to the non-uniform potential energy distribution of solid molecules, symmetric shape of molecules and flatness of the solid surface. The molecular layering increases the strength of the film due to the solid-like, ordered structure of liquid molecules and increases the liquid film thickness. In addition the layering exerts the force (structural force or solvation force) on the solid surfaces. Although this force is small, namely comparable with the van der Waals force, the surfaces deform elastically and the amount of the deformation is of the order of the film thickness. This work offers the observation of the layering effect in the very thin film lubricated contact and shows the EHD calculation in which the solvation force is involved.
The computational chemistry has been mainly used as the support to the experiment especially the visualization of severe conditions are needed. These dangerous or difficult experimental conditions might be reproduced using computer graphics method. Especially, computer chemistry becomes the observation tool for the dynamic behavior of the atoms or molecules. In this paper, we will review our studies on the behavior of molecules in the zeolite nano-pores, the organic molecules in the metal interfaces etc. Recent studies in our laboratory will be also introduced.
Dissociative adsorption of water molecules on Si(001) clean surface becomes a common understanding now. The mechanism, however, has not been clarified yet. This is because it is always tacitly assumed that a water molecule is adsorbed to a surface and dissociates as a monomer. Therefore, we investigated the adsorption of water molecules on Si(001) clean surface based on the first-principles density-functional-theory (DFT) calculations and found that the adsorption energy as a water cluster dramatically increases at a silicon down-dimer site. This adsorption state accompanies a change in quality of hydrogen bond, and the water molecule can be easily dissociated via a proton-relay mechanism. Since this mechanism allows the dissociation between adjacent silicon dimers, the previous experimental results can be explained in more natural ways. We also obtained the result that implies the generality of this mechanism by analyzing of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the water monomer, dimer and Si(001) clean surface based on molecular orbital theory. These theoretical results propose the necessity of taking account of the multi-molecular process as well as the single molecular process.