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Summary: Modeling Proton Transfer in Zeolites: Convergence
Behavior of Embedded and Constrained Cluster
Calculations
Justin T. Fermann,
Teresa Moniz,
Oliver Kiowski,
Timothy J. McIntire,
Scott M. Auerbach,*,, Thom Vreven,§ and Michael J. Frisch§
Departments of Chemistry and Chemical Engineering, UniVersity of Massachusetts,
Amherst, Massachusetts 01003, and Gaussian, Inc., 340 Quinnipiac Street,
Building 40, Wallingford, Connecticut 06492
Received May 2, 2005
Abstract: We have studied the convergence properties of embedded and constrained cluster
models of proton transfer in zeolites. We applied density functional theory to describe clusters
and ONIOM to perform the embedding. We focused on converging the reaction energy and
barrier of the O(1) to O(4) jump in H-Y zeolite as well as vibrational and structural aspects of
this jump. We found that using successively larger clusters in vacuo gives convergence of this
reaction energy to 14 ( 2 kJ mol-1 and the barrier to 135 ( 5 kJ mol-1 at a cluster size of 5 Å,
which contains 11 tetrahedral (Si or Al) atoms. We embedded quantum clusters of various sizes
in larger clusters with total radii in the range 7-20 Å, using the universal force field as the lower
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