Structural, vibrational, and thermal properties of densified silicates: Insights from molecular dynamics

Abstract

Structural, vibrational and thermal properties of densified sodium silicate (NS2) are investigated with classical molecular dynamics simulations of the glass and the liquid state. A systematic investigation of the glass structure with respect to density was performed. We observe a repolymerization of the network manifested by a transition from a tetrahedral to an octahedral silicon environment, the decrease of the amount of non-bridging oxygen atoms and the appearance of three-fold coordinated oxygen atoms (triclusters). Anomalous changes in the medium range order are observed, the first sharp diffraction peak showing a minimum of its full-width at half maximum according to density. The previously reported vibrational trends in densified glasses are observed, such as the shift of the Boson peak intensity to higher frequencies and the decrease of its intensity. Finally, we show that the thermal behavior of the liquid can be reproduced by the Birch-Murnaghan equation of states, thus allowing us to compute the isothermal compressibility.

Fracture toughness of calcium–silicate–hydrate from molecular dynamics simulations

“…Unfortunately, no experimental VDOS is currently available for C-S-H. However, we note that it is very similar to that typically observed in silicate glasses [42], but features additional peaks at high frequency due to the H-O bonds. As expected, the VDOS does not change significantly after the fracture has happened.…”

“…To this end, we compute the vibrational density of state (VDOS) g(ω) before and after the full propagation of the crack. This is achieved by calculating the Fourier-transform of the velocity autocorrelation function (VAF) [42]:…”

Is cement a glassy material?

“…We note that the PDFs of those three systems does not show significant differences that would clearly allow distinguishing a glassy from a crystalline phase. They actually present a similar shape than the PDFs of silicate [21] and chalcogenide glasses [22]. The first peak in the 1Å region is associated to H-O bonds.…”

Thermometer Effect: Origin of the Mixed Alkali Effect in Glass Relaxation

“…All MD simulations were performed using the well-established Teter potential [29][30][31] with an integration timestep of 1 fs. Coulomb interactions were evaluated by the Ewald summation method with a cutoff of 12 Å.…”