Manganese speciation in Mn-rich CaCO3: A density functional theory study

摘要: Abstract The manganese content of aragonitic bivalve shells is a potential archival indicator temporal Mn bioavailability in aquatic environments. speciation mechanism biogenic aragonite minerals remains elusive because the analog challenging to synthesize, and metastable phase has yet be fully resolved experimentally. In this study, we performed density functional theory (DFT) computations hypothetical Mn-doped examine its local coordination structure thermodynamic electronic properties. Our DFT calculations reproduced experimental crystal structures solubility product constants (Ksp) calcite. magnetic moment was close 5 μB both calcite (Ca1−xMnxCO3). calculated Ksp higher than that increased with content, indicative unfavorable coprecipitation phase. We found incorporation small mole fraction into created significant structural distortion around site, resulting mixed numbers (mainly five seven). Valence-to-core X-ray emission spectroscopy (XES) measurements are useful determining environment complexes. theoretical XES spectra, 1s core hole Mn, for four versions aragonite. Boltzmann-averaged spectrum different akin an shells. energy position Kβ2,5 band insensitive CaCO3; however, intensity relatively sensitive speciation. decreased exponentially increasing Mn–O distance. This quantitative relationship report can reduce uncertainties spectral interpretation due absence reference spectrum.