THEORETICAL RESULTS FOR $(H_{2}O)_{n}H^{+}$ AND $(H_{2}O)_{n}$: QMC FOR $H_{5}O_{2}^{+}$, GRAPH THEORETICAL ENUMERATION OF DISTINCT HYDROGEN-BONDED ARRANGEMENTS, COMPACT TO EXTENDED PHASE TRANSITIONS IN $(H_{2}O)_{n}H^{+}$

Abstract

Our recent progress in the study of protonated and neutral water clusters, $(H_{2}O){n}H^{+}$ AND $(H{2}O){n}$, in reviewed. Both variational and diffusion Monte Carlo calculations have been performed, leading to a prediction of the fundamental frequency for motion of the central proton in $H{5}O_{2}^{+}$. {Ab initio} electronic structure calculations suggest this absorption feature will be intense. Extensive Monte Carlo simulations of larger hydrated proton clusters indicate there is a transition between campact and extended phases. Local minima of the potential energy surface for $(H_{2}O){n}H^{+}$ AND $(H{2}O)_{n}$ are studied. The number of topologically distinct hydrogen-bonded arrangements can be enumerated using graph theory, leading to a prediction of the number of distinct local minima of the potential energy surface in compact geometries, including dodecahedral clathrate structures.