Ab initio valence force field calculations for quartz

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Authors:McMillan, P. F.; Hess, A. C.
Author Affiliations:Primary:
Arizona State Univ., Tempe, AZ, United States
Volume Title:Physics and Chemistry of Minerals
Source:Physics and Chemistry of Minerals, 17(2), p.97-107. Publisher: Springer-Verlag, Berlin-New York, Federal Republic of Germany. ISSN: 0342-1791
Publication Date:1990
Note:In English. 52 refs.; illus. incl. 6 tables
Summary:The authors have derived valence force constants for the tetrahedral SiO4 unit and the inter-tetrahedral SiOSi linkage from previous ab initio orbital calculations on H4SiO4 and H6Si2O7 using a split-valence polarized Gaussian basis set (6-31G*), and used these to calculate the IR and Raman active vibrational modes of alpha-quartz. The calculation gives frequencies approx 15% greater than experiment, as expected from harmonic force constants obtained at this level of Hartree-Fock theory, but the calculation gives the correct distribution of modes within each frequency range. Calculated 28-30Si and 16-18O isotope shifts and P shifts to 6 GPa are also in reasonable agreement with experiment. The present authors have also used their ab initio force field to calculate the vibrational spectrum for beta -quartz. The results suggest either that inclusion of a torsional force constant is important for determining the stability of this high-T polymorph, or that the beta -quartz has a disordered structure with lower symmetry (P62) domains, as suggested by earlier diffraction studies. [Authors' abstract] [P.Br.]
Subjects:Framework silicates; Physical properties; Quartz; Silica minerals; Silicates
Abstract Numbers:90M/3907
Record ID:1994030999
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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