粘土鉱物構造中の電荷分布 : 分子軌道法による計算例

概要

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Charge distribution was calculated for a cluster model of clay minerals using a semi-empirical molecular orbital method (Modified Neglect of Differential Overlap, MNDO). The cluster model was constructed with 4 Si, 4 Al, 22 O, and 16 H atoms, so as to represent a part of 2 : 1 type silicate. The calculation showed that the negative charge on the surface O atom tends to decrease, rather than to increase, by isomorphous substitution in both terahedral (Al for Si) and octahedral (hypothetical divalent cation for Al) sheets. It showed, also, that the excess electron due to dissociation of H+ from an edge SiOH group is distributed mainly and nearly equally on the original O and Si atoms, and some on the Si and Al atoms in the neighborhood. The above finding is contrary to the view that the excess electron arising from isomorphous substitution or dissociation of H^+ from crystal edge is localized on the limited number of surface O atoms adjacent to the sites of substitution or dissociation. We propose that the finding be taken into account in the study of interaction between clay minerals and other substances such as ions and compounds.
日本粘土学会の論文
1990-02-27