Molecular Dynamics Evaluation of Dielectric Constant Mixing Rules for H2O-CO2 at Geologic Conditions

Published

October 27, 2015

Author(s)

Raymond D. Mountain, Allan H. Harvey

Abstract

Modeling of mineral reaction equilibria and aqueous-phase speciation of C-O-H fluids requires the dielectric constant of the fluid mixture, which is not known from experiment and is typically estimated by some rule for mixing pure-component values. In order to evaluate different proposed mixing rules, we calculate the dielectric constant from molecular dynamics simulation of a model H2O-CO2 mixture at temperatures of 700 K and 1000 K at pressures up to 3 GPa. We find that theoretically based mixing rules that depend on combining the polarizations of the pure fluids systematically overestimate the dielectric constant of the mixture, as would be expected for mixtures of nonpolar and strongly polar components. The commonly used semiempirical mixing rule due to Looyenga works well for this system at the lower pressures studied, but somewhat underestimates the dielectric constant at higher pressures and densities, especially at the water-rich end of the composition range.

Citation

Journal of Solution Chemistry

Pub Type

Journals

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DOI Link

Keywords

carbon dioxide, dielectric constant, geochemistry, mixtures, polarization, relative permittivity, water

Citation

Mountain, R. and Harvey, A. (2015), Molecular Dynamics Evaluation of Dielectric Constant Mixing Rules for H2O–CO2 at Geologic Conditions, Journal of Solution Chemistry, [online], https://doi.org/10.1007/s10953-015-0401-6 (Accessed November 8, 2024)