Structural transitions and dipole moment of water clusters (H2O)n=4–100

Abstract

The properties of water clusters (H2O)n over a broad range of sizes (n=4–100) were studied by microcanonical parallel tempering Monte Carlo and replica exchange molecular dynamics simulations at temperatures between 20 and 300 K, with special emphasis in the understanding of relation between the structural transitions and dipole behavior. The effect of the water interaction potential was analyzed using six nonpolarizable models, but more extensive calculations were performed using the TIP4P-ice water model. We find that, in general, the dipole moment of the cluster increases significantly as the cluster melts, suggesting that it could be used to discriminate between the solidlike and liquidlike phases. The effect of a moderate electric field on the cluster heat capacity and total dipole moment was found to be negligible.

The Influence of Temperature on C153 Steady-State Absorption and Fluorescence Kinetics in Hydrogen Bonding Solvents

“…In aqueous ClH and PPN the decrease in T changes the equilibrium between free C153 molecules concentration and C153+H 2 O complexes in favor of the former ones. This is related to the fact water forms clusters of the size increasing with decreasing T [12,25], thus reducing the concentration of water molecules accessible for C153 to form complexes. The difference in M e→g and k nr must be small for C153 and its complex with water and we observe an average result as the decay time.…”

Nuclear quantum effects on the structure and the dynamics of [H2O]8 at low temperatures

“…43 Considering their hydrogen bond (HB) connectivity pattern, both isomers present four water molecules acting as double-donor-single acceptors (DDSA) while the other four act as single-donor-double-acceptors (SDDA) and exhibit dangling hydrogens (H dng ). From a thermodynamic perspective, computer simulations have already revealed that these aggregates undergo solid-liquid phase transitions in a thermal range spanning, roughly, the 150 K-200 K interval, 31,34,[44][45][46] and that the explicit introduction of quantum nuclear fluctuations shifts the predicted melting temperature down by about 10-20 K. 47,48 Typically, quantum simulation studies for water have been carried out using potential energy surfaces borrowed from classical force fields for the bulk. As a possible improvement, Manolopoulos and co-workers 49 introduced the flexible q-TIP4P/F model, specifically tailored to avoid implicit quantum effects and be implemented in path-integral simulations of water.…”

Infinite swapping in curved spaces

“…In the bottom panel of Fig. 2 we compare the heat capacity computed for (DDW) 30 using RE 76 and PINS54 simulations with the results expected from the deterministic computation in Eq. (7).…”

“…where dX = dx 1 dx 2 · · · dx N , P n is the permutation operator, and idnx(n, k) is the pointer to all the permutations in the coordinate-temperature list associated with temperature k. 24 The symbol x i is used to no-development of INS and PINS 24 is particularly timely, given our own interests in simulating molecular clusters, [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] and the difficulties we have encountered in the process. Molecular clusters seem to have a much richer set of rare-event like thermodynamic behaviors compared to an atomic cluster of equivalent size.…”