TY  - JOUR
A1  - Spiekermann, Georg
A1  - Wilke, Max
A1  - Jahn, Sandro
T1  - Structural and dynamical properties of supercritical H2O-SiO2 fluids studied by ab initio molecular dynamics
JF  - Chemical geology : official journal of the European Association for Geochemistry
N2  - In this study we report the structure of supercritical H2O-SiO2 fluid composed of 50 mol% H2O and 50 mol% SiO2 at 3000 K and 2400 K. investigated by means of ab initio molecular dynamics of models comprising 192 and 96 atoms. The density is set constant to 138 g/cm(3), which yields a pressure of 4.3 GPa at 3000 K and 3.6 GPa at 2400 K. Throughout the trajec[ories, water molecules are formed and dissociated via the network modifying reaction 2 SiOH = SiOSi + H2O The calculation of the reaction constant K- [OH](2)/[H2O][O2-] is carried out on the basis of the experimentally relevant Q ' species notation and agrees well with an extrapolation of experimental data to 3000 K. After quench from 3000 K to 2400 K, the degree of polymerization of the silicate network in the 192-atom models increases noticeably within several tens of picoseconds, accompanied by release of molecular H2O. An unexpected opposite trend is observed in smaller 96-atom models, due to a finite size effect, as several uncorrelated models of 192 and 96 atoms indicate. The temperature-dependent slowing down of the H2O-silica interaction dynamics is described on the basis of the bond autocorrelation function. (C) 2016 Elsevier B.V. All rights reserved.
KW  - Fluid
KW  - SiO2-H2O
KW  - SiO(2)Molecular dynamics
KW  - Polymerization
KW  - DFT
Y1  - 2016
U6  - https://doi.org/10.1016/j.chemgeo.2016.01.010
SN  - 0009-2541
SN  - 1878-5999
VL  - 426
SP  - 85
EP  - 94
PB  - Elsevier
CY  - Amsterdam
ER  -