Hydrogen bonds(HBs)are weak,generally intermolecular bonds,which hold much of soft matter together.The small mass of hydrogen means that they are inherently quantum mechanical in nature,though all too often these effects are not considered.As a prominent example,a clear picture for the impact of quantum nuclear effects(QNEs)on the strength of HBs and consequently the structure of hydrogen bonded systems is still absent.Using ab initio path integral molecular dynamics(PIMD)[1-3],we show that QNEs weaken weak HBs but strengthen relatively strong ones [1].