Indirect Attractions between Superionic Di-interstitial Protons on Mid-Oxygens in Water at Extreme Conditions: First-Principles Molecular Dynamics Study

The first principles molecular dynamics study enables us to elucidate attractions between the di-interstitial protons on mid-oxygens in superionic water at an extreme high pressure and the temperature. The present analyses elucidate the existence of inner and outer bonded interstitial protons around oxygens and reveal two types of attractions between the protons and oxygens in the water. One is a covalent attraction between them which induces a covalent bonded indirect attraction between the di-interstitial protons on the mid-oxygens. The other is a Coulomb attraction between them which induces a Coulomb type indirect attraction between the di-interstitial protons on the mid-oxygens. The indirect attractions decrease the impurity diffusion of the protons which reduces Haven's ratios of the protons in the water. The negligible amount of the instantaneously formed proton dimers indicates a failure of the caterpillar diffusion mechanism or the Frenkel-Kontorova model for the water. The incomplete electron transfer from the protons to the oxygens reduces the Coulomb atraction between the ionized oxygens and the protons which weakens the sublattice of the mobile protons with smaller mass and size than the oxygens.