First-principles-based simulation of interlayer water and alkali metal ions in weathered biotite

We performed first-principles-based simulations of weathered biotites (WBs) including alkali metal ions to investigate the adsorption states of interlayer cations and the cation/water distribution in their interlayer. Our simulations suggest that the inclusion of Fe³⁺ ions in octahedral sheets of WBs alters significantly the vibrational states, the adsorption states of alkali ions, and the cation/water distribution in our WBs. The Al-O bond cleavage suggested to occur in Fe³⁺-rich regions of WBs upon the H₂O adsorption on Al³⁺ in tetrahedral sheets enhances greatly the dipole moment of adsorbed H₂O molecules, thus enhancing the preference for aggregating inner-sphere complexes of heavy alkali ions particularly Cs⁺.