Quantum tunnelling pathways of the water pentamer

• Published in: Physical chemistry chemical physics : PCCP 2020-01, Vol.22 (3), p.135-144
• Main Authors: Cvitaš, Marko T, Richardson, Jeremy O
• Format: Article
• Language: English
• Subjects: Bifurcations; Hydrogen bonding; Instantons; Quantum tunnelling; Trimers
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c9cp05561d

We apply the semiclassical instanton method to calculate all feasible tunnelling pathways in the water pentamer. Similarly to the water trimer, there are labile flip dynamics as well as a number of different bifurcation pathways coupled to flips. In contrast to the trimer, the puckering motion of the oxygen ring makes the ring-polymer instanton approach difficult to converge, a problem which is resolved by using a recently developed time-independent formalism of the method. We use the results to predict the complete ground-state tunnelling splitting pattern of 320 states, which should help in the continuing effort to assign the experimental spectrum. A comparison between the rearrangement pathways in the water trimer and pentamer sheds light on the many-body cooperative effects of hydrogen bonding which are important for a full understanding of the liquid state. Five tunnelling rearrangement pathways in water pentamer are responsible for the ground-state tunnelling splitting pattern of 320 states.