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Title: Ab Initio Molecular Dynamics Simulation of Divalent Metal Cation Incorporation in Calcite: Implications for Interpreting X-ray Absorption Spectroscopy Data

Journal Article · · ACS Earth and Space Chemistry
ORCiD logo [1]; ORCiD logo [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical and Computational Sciences Directorate
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Calcite (CaCO3) is a ubiquitous mineral with the ability to accommodate a wide range of impurities. Determination of the coordination environment and incorporation modes of impurities in calcite has historically relied primarily on the interpretation of extended X-ray absorption fine structure (EXAFS) spectroscopy. However, lack of standards combined with the large number of degrees of freedom involved in shell-by-shell fits have made the interpretation of EXAFS spectra challenging. As such, in this work, ab initio molecular dynamics (AIMD) simulations were performed to investigate the incorporation of seven divalent metal cation impurities, namely, Ba2+, Pb2+, Sr2+, Cd2+, Mn2+, Co2+, and Zn2+, in calcite. These cations span a wide range of sizes: 30.7 to –22.8% change in ionic radius with respect to Ca2+. The atomic trajectories were then used to compute EXAFS spectra for direct comparison with published experimental spectra. The simulations confirmed that all seven metal cations incorporate in calcite via substitution in the calcium site. The AIMD–EXAFS approach allowed for overcoming limitations of the shell-by-shell fitting approach, such as the difficulties in resolving weak backscatterers beyond the first coordination shell. As a result, the AIMD–EXAFS approach was able to provide a detailed and comprehensive characterization of the structural relaxation around divalent metal cation impurities in calcite.

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States). Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division; USDOE Office of Science (SC), Biological and Environmental Research (BER)
Grant/Contract Number:
AC05-76RL01830
OSTI ID:
1574896
Report Number(s):
PNNL-SA-146667
Journal Information:
ACS Earth and Space Chemistry, Vol. 3, Issue 11; ISSN 2472-3452
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

Figures / Tables (12)

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
calcium carbonate
ab initio molecular dynamics
extended x-ray absorption fine structure spectroscopy
isovalent substitution
impurity incorporation
structural relaxation
ST4