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 Fe(3+) 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 Fe(3+)-rich regions of WBs upon the H2O adsorption on Al(3+) 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(+).