Bonding, structural and thermodynamic analysis of dissociative adsorption of HO ion onto calcite (101⁻4) surface: CPMD and DFT calculations.

We used density functional theory (DFT) and Car-Parrinello molecular dynamics (CPMD) simulation to investigate the adsorption and bond formation of hydronium ion (HO) onto a [Formula: see text] calcite surface. For surface coverage of 25% to 100%, the nature of HO interaction was explored through electron density and energetics in the context of bond critical points. The adsorbate-adsorbent structure was studied by simulation of pair correlation function. The results revealed that dissociation into water molecule(s) and proton(s) complements HO ion(s) adsorbtion. The HO molecule adsorbs onto the surface via its O atom, and interacts with surface calcium in a closed-shell mode; the H ion makes a covalent bond to the surface oxygen while maintaining H-bonding with water. Adsorption energies were diminished by 70-90 kJ mol when O-bonded H ions transferred to the O manually. While dissociative adsorption of HO ions is spontaneous at all surface coverages tested, the free energy was lowest at 75% coverage. Also, protonation of a completely pre-hydrated calcite surface leads to stronger interaction of water molecules with the surface. This unique outlook on hydrating calcite provides specific insights into biomineralization of this mineral, and helps depict further pH consequences in the field of biomaterial adsorption. Graphical abstract Dissociative adsorption of hydronium ion onto the surface of calcite.