Analysis of the structural H/D isotope effect with an excess proton/deuteron in light/heavy water solvent using path integral molecular dynamics simulations

We analyzed the difference in the structural H/D isotope effect between an excess proton in light water (H-body) and an excess deuteron in heavy water (D-body), including the nuclear quantum effect, using path integral molecular dynamics simulations. We found that the second peak of the H-body is shorter than that of the D-body in the radial distribution function of O^*-O, where O^* is the oxygen atom of the H₃O⁺/D₃O⁺ fragment. The main reason for this would be the difference in the ratio of the Zundel structure with the sp³ -like configuration, where the Zundel structure in the H-body (14.0%) is greater than that in the D-body (12.0%). We also found rare occurrences of double H₃O⁺/D₃O⁺ configurations, mainly including Zundel-Zundel-like structures such as H₇O₃⁺/D₇O₃⁺ and H₉O₄⁺/D₉O₄⁺. The ratios of such configurations appearing in our simulations are 0.89% and 0.20% for the H-body and the D-body, respectively. (author)