SREL Reprint #2152

 

 

 

 

Molecular Dynamics Modeling of Clay Minerals. 1. Gibbsite, Kaolinite, Pyrophyllite, and Beidellite

Brian J. Teppen,1 Kjeld Rasmussen,2 Paul M. Bertsch,1 David M. Maler,3 and Lothar Schafer4

1Advanced Analytical Centerfor Environmental Sciences, Savannah River Ecology Laboratory, University of Georgia, P.O. Drawer E, Aiken, South Carolina 29802,
2Department of Chemistry, Building 207, The Technical University of Denmark, DK-2800 Lyngby, Denmark,
3Department of Agronomy, 115 Plant Science Building, University of Arkansas, Fayetteville, Arkansas 72701, and
4Department of Chemistry and Biochemistry, 115 Chemistry Building, University of Arkansas, Fayetteville, Arkansas 72701

A molecular dynamics model for clays and the oxide minerals is desirable for studying the kinetics and thermodynamics of adsorption processes. To this end, a valence force field for aluminous, dioctahedral clay minerals was developed. Novel aspects of this development include the bending potential for octahedral O-Al-0 angles, which uses a quartic polynomial to create a double-well potential with minima at both 90º and 180º. Also, atonidc point charges were derived from comparisons of ab initio molecular electrostatic potentials with X-ray diffraction-based deformation electron densities. Isothermal-isobaric molecular dynamics simulations of quartz, gibbsite, kaohnite, and pyrophyllite were used to refine the potential energy parameters. The resultant force field reproduced all the major structural parameters of these minerals to within 1% of their experimentally determined values. Transferability of the force field to simulations of adsorption onto clay mineral surfaces was tested through simulations of Na+, Ca2+, and hexadecyltrimethylainmonium (HDTMA+) in the interlayers of beidellite clays. The new force field worked rather well with independently derived nonbonded parameters for all three adsorbates, as indicated by comparisons between experimental and molecular-dynamics-preclicted d(00l) layer spacings of the homoionic beidellites.

SREL Reprint #2152

Teppen, B.J., K. Rasmussen, P.M. Bertsch, D.M. Miller, and L. Schafer. 1997. Molecular dynamics modeling of clay minerals. 1. gibbsite, kaolinite, pyrophyllite, and beidellite. Journal of Physical Chemistry 101:1579-1587.

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