Molecular dynamics studies of the vitreous state: Simple ionic systems and silica

L. V. Woodcock, Charles Angell, P. Cheeseman

Research output: Contribution to journalArticle

506 Citations (Scopus)

Abstract

Some applications of molecular dynamics calculations to the vitreous state have been examined for simple ionic MX and MX2 type glasses. The MX system which corresponds to a hypothetical vitreous and supercooled amorphous KCl is found to undergo an isobaric transition in the region of 0.3 T f and an isothermal transition at around 35 kbar (T = Tf). The transition is evidenced by a discontinuity in second order thermodynamic properties and may be associated with a virtual disappearance of translational diffusion. By employing a variety of irreversible stress histories, the vitreous state in this case is shown to be insensitive to the thermodynamic stress history up to a maximum computationally permissible relaxation time of around 10-10 sec. Simulations are also reported for some ionic liquids of MX2 stoichiometry which, in contrast with KCl, have glass-forming ability (BeF2, ZnCl2, and SiO2). Although the relaxation times involved in laboratory glass formation far exceed the long-time limit of computer "experiment", the configurationally arrested states which are produced by simulation exhibit many characteristic features of the experimental glasses. Changes of heat capacity consequent on configurational arrest in the case of KCl are similar in magnitude to those observed at the experimental glass transition of simple ionic glasses. The radial distribution for simulated SiO2 "glass" is very similar to that for vitreous silica, and a simulated compression-vitrification-expansion cycle for this system produces a "densified" glass, as observed in laboratory experiments. A rattle-and-correlated-jump mechanism appears suitable for the description of diffusion in this liquid. Limitations and further applications of MD calculations pertaining to the vitreous state are discussed.

Original languageEnglish (US)
Pages (from-to)1565-1577
Number of pages13
JournalThe Journal of Chemical Physics
Volume65
Issue number4
StatePublished - 1976
Externally publishedYes

Fingerprint

Silicon Dioxide
Molecular dynamics
molecular dynamics
silicon dioxide
Glass
glass
Relaxation time
Diffusion in liquids
relaxation time
Ionic Liquids
histories
Vitrification
vitrification
Fused silica
Stoichiometry
liquids
Specific heat
Glass transition
radial distribution
Thermodynamic properties

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Molecular dynamics studies of the vitreous state : Simple ionic systems and silica. / Woodcock, L. V.; Angell, Charles; Cheeseman, P.

In: The Journal of Chemical Physics, Vol. 65, No. 4, 1976, p. 1565-1577.

Research output: Contribution to journalArticle

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