Crystal-chemical, vibrational and electronic properties of 1M-phlogopite K(Mg,Fe)3Si3AlO10(OH)2 from Density Functional Theory simulations

Trioctahedral micas are peculiar minerals that may present interesting electronic properties that can be modulated by specific cationic substitutions. In the present work, a detailed characterization of the structural, vibrational, and electronic properties of 1M-phlogopite as a function of the FeII/MgII substitutions, with Mg/Fe ratio ≥ 2, is reported. The results were obtained from density functional theory simulations at the B3LYP-D* level of theory, which included the effect of long-range interactions, and also using all-electron Gaussian-type orbitals to describe the atoms in the mineral. The crystal structures of the different phlogopite models were in good agreement with previous X-ray and neutron diffraction data reported in the literature. In addition, the simulated Raman spectra well described the experimental ones obtained from confocal Raman micro-spectrometry, providing additional information on the atomic motions. The electronic band structure and the atom- and orbital-projected density of states were also discussed, describing the nature of the band gap and electronic transitions, and how they vary with the iron content.