Density Functional Study of Structural and Vibrational Properties of α-Moganite

Abstract

α-moganite is a recently discovered polymorph of silica, commonly intergrown with quartz in natural microcrystalline silica samples. An important challenge is finding an effective method for estimating its amount in a sample under study, which is important for its applications, related to the technology of growth of dielectric layers, as well as for fundamental problems, related to the formation of both terrestrial and lunar mineral deposits and biogenic formation. One of these methods is vibrational spectroscopy, with the help of which the presence of a particular compound is determined by the presence of characteristic spectral lines. In this work, the search for such lines is carried out using density functional theory calculations and comparisons of the IR and Raman spectra of α-quartz and α-moganite. With the help of such calculations, the stability of the moganite structure has been proven for the first time, and its spectral characteristics have been determined over the entire range of vibrational frequencies. Several new spectral lines characteristic of α-moganite were discovered in the 65–85 cm−1 region. Moreover, the evolution of spectral peculiarities under hydrostatic pressure was studied.

Differentiating α-moganite, silanol and α-quartz by Raman spectroscopy

“…Simulation results represent reasonably well the balance of relative intensity of spectral features, however, uncertainty in the relative intensity remains particularly for bands near 200 cm −1 (Fig. 2a), where simulated Raman spectra have a higher intensity than observed in measurements from other studies, 24 but the reversed situation is seen in this study (Fig. 2b).…”

“…This can be explained by crushing and reducing grain size thereby creating fresh surfaces and increasing surface area and hence silanol, and also by exposing silanols originally inherited by internal surfaces or in pore spaces but now physically exposed during sample preparation. 24…”

DFT Study of Charge Transfer Complexes Between Norfloxacin and Ciprofloxacin Drugs with Picric Acid and 3,5-Dinitrobenzoic Acid Acceptors

“…This is because the resulting spectra contain numerous bands that overlap. Thus, vibrational frequency calculations help identify spectral characteristics [21,22]. Additionally, the animations of various vibrational modes simplify the process of assigning them.…”