Journal ArticleDOI
Theoretical investigation of moganite
Ute Hantsch,Björn Winkler,Chris J. Pickard,Julian D. Gale,M. C. Warren,Victor Milman,Francesco Mauri +6 more
TLDR
The structure and properties of two different modifications of moganite have been studied using density functional theory, and the results have been compared to quartz as mentioned in this paper, and it is shown that the enthalpy difference between the two is negligible.Abstract:
The structure and properties of two different modifications of moganite have been studied using density functional theory, and the results have been compared to quartz. It is shown that the enthalpy difference between quartz and moganite, whose structure can be understood as Brazil twinning of quartz on a unit cell length scale, is negligible. This explains the significant amount of moganite in fine-grained quartz samples, as well as the frequent occurrence of Brazilian twinning in quartz. The compression mechanism of moganite has been elucidated, and it is argued that moganite is significantly more compressible than quartz. Observed and calculated NMR spectra are compared, and it is found that the bonding in quartz and moganite is very similar, consistent with the results of a Mulliken population analysis. The elastic stiffness coefficients of moganite have been predicted, and it is shown that formal-charge shell model interatomic potentials appear to be more transferable from quartz to moganite than partial-charge rigid ion equivalents.read more
Citations
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Journal ArticleDOI
Crystal structure transformations in SiO2 from classical and ab initio metadynamics.
TL;DR: A substantial improvement of the metadynamics method is introduced, which finally brings simulations in close agreement with experiments and unveils the subtle and non-intuitive stepwise mechanism of the pressure-induced transformation of fourfold-coordinated α-quartz into sixfold- coordinated stishovite at room temperature.
Journal ArticleDOI
Infrared absorption spectroscopy of SiO2-moganite
TL;DR: In this article, the spectral properties of moganite and fine-grained quartz were analyzed using absorption infrared spectroscopy (IR) and the results indicated that moganites and α-quartz have different crystal structures and symmetries in terms of different tetrahedral linkages.
Journal ArticleDOI
Structure–property relations and thermodynamic properties of monoclinic petalite, LiAlSi4O10
Eiken Haussühl,Jürgen Schreuer,Björn Winkler,Siegfried Haussühl,Lkhamsuren Bayarjargal,Victor Milman +5 more
TL;DR: Structure-property relations of monoclinic petalite, LiAlSi(4)O(10), were determined by experiment and atomistic modeling based on density functional theory to predict electric field gradients, the lattice dynamics and thermodynamic properties.
Journal ArticleDOI
Synthesis of nanocrystalline low temperature silica polymorphs
TL;DR: In this article, high pressure conversion of colloidal silica has been performed at temperatures between 125 and 220°C at 100 MPa water pressure for 5 to 90 days, and the final synthesis product was low quartz ( α -quartz) in all cases.
Journal ArticleDOI
Pressure–induced crystallization of biogenic hydrous amorphous silica
TL;DR: In this article, the diatom Nitzschia cf. frustulum was collected from Lake Yogo, Siga Prefecture, Japan, and the remaining frustules were studied by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared (FTIR) spectrograms, and synchrotron Xray diffraction.
References
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Journal ArticleDOI
Generalized Gradient Approximation Made Simple
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Projector augmented-wave method
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Inhomogeneous Electron Gas
P. C. Hohenberg,Walter Kohn +1 more
TL;DR: In this article, the ground state of an interacting electron gas in an external potential was investigated and it was proved that there exists a universal functional of the density, called F[n(mathrm{r})], independent of the potential of the electron gas.
Journal ArticleDOI
Soft self-consistent pseudopotentials in a generalized eigenvalue formalism.
TL;DR: Novel features are that the pseudopotential itself becomes charge-state dependent, the usual norm-conservation constraint does not apply, and a generalized eigenproblem is introduced.