Asymmetric hydrogen bonding in formic acid–nitric acid dimer observed by quantum molecular dynamics simulations
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Heterodimer of formic acid and nitric acid, of which the monomer acidity has large difference, was studied by on-the-fly ab initio molecular dynamics (AIMD) and path integral molecular dynamics (PIMD) simulations with RI-BVWN/SVP level of density functional theory, to elucidate the nuclear quantum effect and isotopic effect on the structural dynamics of the heterodimer. At 300 K, the two hydrogen bonds were maintained in both AIMD and PIMD regimes. Analyses in structural parameters suggested that this heterodimer should exist in the asymmetric binding mode, where hydrogen bonding is stronger on the C=O…H–O–N side. The asymmetry in the binding can be observed even more when the nuclear quantum effect was introduced. Although the complex has an equal conformation connected by a double hydrogen bonding, analyses in the principal component modes revealed the dominance of the dimer opening and twisting motions, which were suggested to obstruct double-proton transfer.
KeywordsFormic acid–nitric acid dimer Path integral molecular dynamics simulation Nuclear quantum effect Isotopic effect Hydrogen bond
This authors wish to acknowledge Grant-in-aid for Scientific Research (KAKENHI) by Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan (15KT0067 and 16H00780); and Thailand Research Fund (MRG5980189 and RSA5880057) for the financial support. The Department of Chemistry, Faculty of Science, Chiang Mai University, is also acknowledged for the courtesy in management. Theoretical calculations were partly performed at the Research Centre for Computational Science, Institute for Molecular Science, Japan, and Centre of Computational Materials Science, Institute for Solid State Physics, The University of Tokyo, Japan.
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