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Geofluids
Volume 2018, Article ID 4279124, 12 pages
https://doi.org/10.1155/2018/4279124
Research Article

CuCl Complexation in the Vapor Phase: Insights from Ab Initio Molecular Dynamics Simulations

1CSIRO Mineral Resources, Clayton, VIC 3168, Australia
2School of Earth, Atmosphere and Environment, Monash University, VIC 3800, Australia
3Earth and Environmental Division, Los Alamos National Laboratory, M.S. J535, P.O. Box 1663, Los Alamos, NM 87545, USA
4Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC, Canada H3A 0E8

Correspondence should be addressed to Yuan Mei; ua.orisc@iem.nauy

Received 1 December 2017; Accepted 21 March 2018; Published 2 May 2018

Academic Editor: Ferenc Molnar

Copyright © 2018 Yuan Mei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We investigated the hydration of the CuCl0 complex in HCl-bearing water vapor at 350°C and a vapor-like fluid density between 0.02 and 0.09 g/cm3 using ab initio molecular dynamics (MD) simulations. The simulations reveal that one water molecule is strongly bonded to Cu(I) (first coordination shell), forming a linear [H2O-Cu-Cl]0 moiety. The second hydration shell is highly dynamic in nature, and individual configurations have short life-spans in such low-density vapors, resulting in large fluctuations in instantaneous hydration numbers over a timescale of picoseconds. The average hydration number in the second shell (m) increased from ~0.5 to ~3.5 and the calculated number of hydrogen bonds per water molecule increased from 0.09 to 0.25 when fluid density (which is correlated to water activity) increased from 0.02 to 0.09 g/cm3 (H2O 1.72 to 2.05). These changes of hydration number are qualitatively consistent with previous solubility studies under similar conditions, although the absolute hydration numbers from MD were much lower than the values inferred by correlating experimental Cu fugacity with water fugacity. This could be due to the uncertainties in the MD simulations and uncertainty in the estimation of the fugacity coefficients for these highly nonideal “vapors” in the experiments. Our study provides the first theoretical confirmation that beyond-first-shell hydrated metal complexes play an important role in metal transport in low-density hydrothermal fluids, even if it is highly disordered and dynamic in nature.