Signature of small rings in the Raman spectra of normal and compressed amorphous silica: A combined classical andab initiostudy

Abstract

We calculate the parallel (VV) and perpendicular (VH) polarized Raman spectra of amorphous silica. Model SiO2 glasses, uncompressed and compressed, were generated by a combination of classical and ab initio molecular-dynamics simulations and their dynamical matrices were computed within the framework of the density functional theory. The Raman scattering intensities were determined using the bond-polarizability model and a good agreement with experimental spectra was found. We confirm that the modes associated to the fourfold and threefold rings produce most of the Raman intensity of the D1 and D2 peaks, respectively, in the VV Raman spectra. Modifications of the Raman spectra upon compression are found to be in agreement with experimental data. We show that the modes associated to the fourfold rings still exist upon compression but do not produce a strong Raman intensity, whereas the ones associated to the threefold rings do. This result strongly suggests that the area under the D1 and D2 peaks is not directly proportional to the concentration of small rings in amorphous SiO2.

Vibrational properties of a sodium tetrasilicate glass: Ab initio versus classical force fields

“…Recently, a comparison of the Raman scattering mechanism in α-quartz using both ab initio and BPA methods has shown that the BPA reproduces the ab initio Raman intensities within 15% [24]. For amorphous silica models generated by ab initio molecular dynamics simulations, the use of the BPA gives rise to Raman spectra in good agreement with experimental data [25]. This gives strong support for the application of the BPA for the calculation of the Raman spectra of large models of silicate glasses.…”

Calculation of off‐resonance Raman scattering intensities with parametric models

“…The result concerning the 3R rings is in a line with that obtained by Umari and Pasquarello who applied the previously presented ab initio derived BPM parameters of quartz to a 72 atoms system modeled by firstprinciples, where they obtained five 3R rings, but they diverge for the 4R rings where only two 4R rings were present so that a reliable statistics was impossible to obtain. [90] The glass models generated by Rahmani et al [91] with a system of the same size yielded a similar ring distribution and although the spectral analysis was performed somewhat differently the conclusions concerning the D 1 band were not completely convincing. Larger simulation box of 144 atoms was used in a recent study by Giacomazzi et al [92] The conclusions of the work remained similar to those of ref.…”

Molecular dynamics study of the vibrational pattern of ring structures in the Raman spectra of vitreous silica

“…While Pasquarello and Car 20 confirmed the assignment by Galeener et al 14 and Barrio et al 15 and further used it for an estimation of the ring concentration in the glass sample, 21,22 Lazzeri and Mauri 23 came to the conclusion that not all the small rings have decoupled breathing vibrations. Rahmani et al 24 found the existence of concerted ring modes but noticed that the absence of D 1 and D 2 bands does not mean the absence of the corresponding rings, so that the estimation of the concentration proposed by Umari et al 21,22 might not be reliable.…”

“…Making use of the advantage of the numerical experiments, we attempt to apply the model suggested by Galeener et al 14 and Barrio et al 15 in order to calculate the Raman patterns of small rings present in realistic models of a-SiO 2 . The present work uses the strategy of Rahmani et al 24 The vitreous silica structures were generated with the help of potential proposed by Van Beest et al 25 (BKS potential). However, to avoid the size limitations of first-principles methods used in Ref.…”

“…However, to avoid the size limitations of first-principles methods used in Ref. 24, the spectroscopic analysis was carried out with an effective potential 26 recognised for its efficiency in simulating vibrational spectra of aluminosilicates. The size of the studied systems is sufficiently large (more than 1000 atoms), thus avoiding the influence of finite size effects on the calculated characteristics.…”