Density functional study of cluster models of zeolites. 1. Structure and acidity of hydroxyl groups in disiloxane analogs
- Pacific Northwest Lab., Richland, WA (United States)
In this work we calculate the structures and acidities of a series of clusters that mimic terminal and bridging hydroxyl groups in zeolites and molecular sieves using the local density functional (LDF) program DMol. The clusters include silanol, H[sub 3]Si-OH, and its anion, the simplest model of terminal hydroxyl groups at zeolite surfaces and defect sites. We also consider disiloxane, H[sub 3]Si-O-SiH[sub 3], and a series of structural analogs of disiloxane, H[sub 3]T-O(H)-TH[sub 3] (T = tetrahedrally coordinated atom) in which Si is substituted by Al, B, P, Ga, or Ge. The accuracy of these LDF calculations is determined in part by the size of the numerical basis set and quadrature grid. We find that the structures of the clusters are insensitive to increases in quadrature grid size beyond [approx equal] 3000 points/atom. However, the optimized values of the internal coordinates, particularly the T-O-T bond angle, are much more sensitive to basis set size. The largest basis set used in these calculations (DNP+) shows convergence in key internal coordinates to [approx equal] 0.1[degree]-5.0[degrees] for T-O(H)-T bond angles and better than 0.01 A for T-O bond lengths. We also gauge the accuracy of the LDF results against extended basis set Hartree-Fock MP2 results (MP2/DZ+2d) and experimental data. 60 refs., 5 figs., 21 tabs.
- DOE Contract Number:
- FG06-89ER75522; AC06-76RL01830
- OSTI ID:
- 5651362
- Journal Information:
- Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 97:38; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
661000 -- General Physics-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ADSORBENTS
DATA
EXPERIMENTAL DATA
HYDROXYL RADICALS
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
MATHEMATICAL MODELS
MINERALS
MOLECULAR MODELS
MOLECULAR SIEVES
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC SILICON COMPOUNDS
PH VALUE
RADICALS
SILICATE MINERALS
SILOXANES
SOLID CLUSTERS
ZEOLITES