Universität zu Köln

Spiekermann, Georg, Wilke, Max ORCID: 0000-0002-1890-3940 and Jahn, Sandro ORCID: 0000-0002-2137-8833 (2016). Structural and dynamical properties of supercritical H2O-SiO2 fluids studied by ab initio molecular dynamics. Chem. Geol., 426. S. 85 - 95. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1872-6836

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Abstract

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.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Spiekermann, Georg UNSPECIFIED UNSPECIFIED UNSPECIFIED Wilke, Max UNSPECIFIED orcid.org/0000-0002-1890-3940 UNSPECIFIED Jahn, Sandro UNSPECIFIED orcid.org/0000-0002-2137-8833 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-275728
DOI:	10.1016/j.chemgeo.2016.01.010
Journal or Publication Title:	Chem. Geol.
Volume:	426
Page Range:	S. 85 - 95
Date:	2016
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1872-6836
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language 1ST PRINCIPLES SIMULATIONS; DENSITY-FUNCTIONAL THEORY; CRITICAL END-POINT; SILICATE MELTS; COMPLETE MISCIBILITY; AQUEOUS FLUIDS; LIQUID WATER; UPPER-MANTLE; PRESSURE; MECHANISMS Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/27572