Quantum Stabilization of the Frustrated Hydrogen Bonding Structure in the Hydrogen Fluoride Trimer.

We performed ab initio path integral molecular dynamics (PIMD) and molecular dynamics (MD) simulations to discuss the thermal and nuclear quantum effects on the stabilities of hydrogen bonding network in a hydrogen fluoride trimer (HF)3 cluster. By the conventional molecular orbital calculation, the (HF)3 cluster has an equilateral triangle shape, which has a frustration in the chemical structure of the hydrogen bonds, whereas the hydrogen bonding structure of a hydrogen fluoride dimer (HF)2 cluster is nearly perpendicular to the acceptor molecule. The ratio of the triangular structures with the three hydrogen bondings in the PIMD simulation is larger than that in the MD one, whereas nonhydrogen bonding conformations such as a dimerlike structure are often found in MD simulation. The nuclear quantum effect stabilizes the frustrated hydrogen bonding network of the triangular (HF)3 cluster.