Ab initio calculations of relative stabilities of different structural arrangements in dioctahedral phyllosilicates

Authors: Tunega, Daniel; Goodman, Bernard A.; Haberhauer, Georg; Reichenauer, Thomas G.; Gerzabek, Martin H.; Lischka, Hans

Source: Clays and Clay Minerals, Volume 55, Number 2, April 2007 , pp. 220-232(13)

Publisher: The Clay Minerals Society

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Abstract:

An ab initio theoretical approach has been used to calculate optimized geometries and the relative energies of various compositional arrangements in structures of dioctahedral smectites based on models consisting of two unit-cells. These calculations indicate that the energy differences between structures having vacancies in sites with cis- or trans-OH coordination are small and that their relative energies vary with the chemical nature of the substitutions. For example, a cis-OH coordination for the vacancy was the most stable when the interlayer charge originated from substitution of Al for Si in the tetrahedral sheet, whereas the trans-coordination was the more stable for most cases of substitution in the octahedral sheet, an exception being Fe(II) for Al where the cis-OH coordination was favored. It seems likely, therefore, that long-range structural disorder will be a common phenomenon in natural phyllosilicate specimens.

Keywords: AB INITIO; DIOCTAHEDRAL; PHYLLOSILICATES; SMECTITE; CIS- AND TRANS-COORDINATION

Document Type: Research article

DOI: http://dx.doi.org/10.1346/CCMN.2007.0550211

Publication date: 2007-04-01

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Ab initio calculations of relative stabilities of different structural arrangements in dioctahedral phyllosilicates

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