High-pressure behavior of 2M1 muscovite

Abstract

The crystal structure and pressure influence (between 0-6 GPa) on 2M 1 muscovite have been calculated by quantum-mechanical methods based on density functional theory (DFT) with optimized numerical LCAO basis sets and norm-conserving pseudopotentials. Tensions between 0.8 and 0 GPa have been also studied. Volumes as a function of pressure, computed from the generalized gradient approximation, are closer to the experimental data than volumes calculated from the local density approximation. The crystal structure, bond distances, and main geometrical features agree with previous experimental values. A third-order Birch-Murnagham equation is fitted, giving a bulk modulus of 60.1 GPa, which reasonably agrees with the experimental data. Axis compressibilities are slightly smaller than those of the experimental data. The most compressible axis is the c axis. Bond strains, angles, the main geometrical features, and polyhedral strains are studied as a function of pressure, and these vary according to the experimental behavior. Tetrahedral <α> and <ρ 2 > angles and corrugation show an oscillating behavior in the range of pressures used. The most important compressibilities are those related to the interlayer space, as it corresponds to the weakest bonding in the structure. The highest compressibility in the T-O-T layer along the [001] direction is determined by the octahedral sheet thickness. The compressibilities along the a and b axes are determined by the tetrahedra, as the most compressible polyhedra, and the α angle. Therefore, with our results the utility of periodic DFT methods for studying crystal structure and the effect of hydrostatic pressure on 2M 1 muscovite are once again validated, and they are suitable to describe the compression of the crystal structure in detail.

Computational study of the elastic behavior of the 2M1 muscovite-paragonite series

“…The pseudopotentials and basis sets used in this work were previously optimized for a set of dioctahedral 2:1 phyllosilicates (Ortega-Castro et al 2008). In a previous paper (Ortega-Castro et al 2010), the high-pressure behavior of Ms was calculated in both the local density approximation (LDA) with the Ceperley-Alder exchange-correlation functional (Ceperley and Alder 1980) and GGA-PBE approach, finding that the GGA yielded cell parameters closer to the experimental data than did LDA. In addition, White et al (2009) demonstrated that GGA functional showed lower energies and more accurate geometries.…”

“…This rotation is defined by the α angle. Crystal chemistry, pressure, and temperature affect the α angle (Comodi and Zanazzi 1997;Mercier et al 2006;Ortega-Castro et al 2010).…”

“…Thus, although the elastic properties of minerals are key geophysical data, it is frequently difficult to measure the exact elastic-stiffness constants (ECs), especially in natural minerals where cation order/disorder, morphological, crystal-chemical, and crystal-physical heterogeneities exist (Mondol et al 2008). However, computational methods can yield reliable crystal structures and ECs free of these natural heterogeneities (Karki et al 2001;Stixrude 2002;Stixrude and Peacor 2002;Weirich 2004;Ortega-Castro et al 2010;Militzer et al 2011). This can help explain the crystal-chemical, crystal-physical, mineralogical, and petrological behavior of minerals and aid interpretations of the seismologic data.…”

Dehydroxylation of kaolinite to metakaolin—a molecular dynamics study

“…To accelerate the process it is necessary to fully understand the mechanisms that govern dehydration. Research has generally focused on the dehydration behaviour of the group of clay minerals classified as 2:1 dioctahedral aluminous phyllosilicates, such as the smectites, montmoronillonites, illites and vermicullites [1][2][3][4][5][6][7][8][9] . Typically the dehydroxylation of these materials is produced by a combination of two independent processes that occur in the calcination process 1,[10][11][12][13][14][15] : (1) the continuous loss of interlayer water (dehydration) and (2) the discontinuous loss of structural water (dehydroxylation).…”

Theoretical study on the influence of the Mg2+ and Al3+ octahedral cations on the vibrational spectra of the hydroxy groups of dioctahedral 2:1 phyllosilicate models

“…No significant difference in the main lattice parameters was detected between these arrangements (Table 1). According to previous studies [49], the most stable arrangement is the meta configuration and the least stable is the ortho configuration. The difference in energy with respect to the meta configuration can be related to the distance between Mg 2+ in the octahedral lattice.…”