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Ab initio investigation of majorite and pyrope garnets; lattice dynamics and vibrational spectra

Marco de la Pierre and Donato Belmonte
Ab initio investigation of majorite and pyrope garnets; lattice dynamics and vibrational spectra
American Mineralogist (January 2016) 101 (1): 162-174

Abstract

A detailed ab initio quantum-mechanical characterization is presented of the vibrational properties of pyrope and majorite garnets, using the hybrid B3LYP functional and large all electron Gaussian type basis sets. Discussed quantities include infrared (both TO and LO) and Raman frequencies, normal mode coordinates, spectroscopic intensities, mode Gruneisen parameters, isotopic substitution, and infrared and Raman spectra. Comparison with data available in the literature demonstrates the accuracy of the adopted method. Main spectral features of the two garnets are interpreted in terms of either symmetry analysis or structural contributions to the vibrational modes. Missing peaks in the experiments are discussed in light of the simulated spectra. The present high-quality vibrational data can be used to compute thermal expansivities at high-pressure and high-temperature conditions. Calculated values for majorite at the bottom of the mantle transition zone (alpha V=2.2X10 (super -5) K (super -1) at T=1500 K and P=20 GPa) turn out to be sensibly greater (up to three times) than those currently adopted in geophysical thermodynamic databases, thus calling for a careful revision of the numerical models for thermo-chemical convection of the Earth's mantle.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 101
Serial Issue: 1
Title: Ab initio investigation of majorite and pyrope garnets; lattice dynamics and vibrational spectra
Affiliation: Curtin University, Department of Chemistry, Perth, West. Aust., Australia
Pages: 162-174
Published: 201601
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 97
Accession Number: 2016-025624
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
Secondary Affiliation: Universita di Genova, ITA, Italy
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201613
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