Application of the Molecular Orbital Method for Clay Science

Molecular orbital method can predict the physico-chemical properties and structure of a molecule. The predictions are made by theoretical calculations based on quantum mechanics. Recent developments using computer hard and softwares enable the application of the method to clay minerals. In the input file, some key words are necessary beside the geometrical data of minerals to subsequently complete calculations automatically. Charge distributions of 2:1 type layer silicate minerals were calculated by the molecular orbital method using model clusters. Results showed that the charge on surface oxygen atom did not change following isomorphous substitutions. The molecular orbital method has interpreted the observed relationship between Si/Al ratio and surface acid strength of allophane. It showed that the interaction between silanol group of polymerized silicic acid and the pore moiety of the wall enhanced the degree of dissociation of the silanol group. The molecular orbital method allows us to understand the properties of clay minerals on the basis of electronic states. The studies of clay minerals are expected to develop further by utilizing this theoretical method.