Nuclear Quantum Effects in Chemical Bonding Theory: Inter/Intramolecular Hydrogen-Bonding Interactions

Nuclear quantum effects (NQEs) play a crucial role in a wide range of chemistry, from life science to mate- rial chemistry. This study employs the approaches based on the Born-Oppenheimer quantum chemistry calculations and the beyond and investigates NQEs in inter/intra- molecular hydrogen-bonding interactions. The chemical bond analyses with natural bond orbital and non-covalent interaction approaches revealed that NQEs generally en- hance hydrogen-bonding interaction for (HX)3 (X=F, OH, NH2), tropolone, malonaldehyde, 9-hydroxyphenalenone, and deuterated species. It was also clarified that hydrogen- bonding interaction in -H species is more ionic (less cova- lent) than in -D. These findings highlight the essential role of NQEs in controlling chemical bonds and have practical implications for designing new materials and understanding biological processes from a molecular electronic states’ point of view.