Lewis-inspired representation of dissociable water in clusters and Grotthuss chains

Abstract

Proton transfer to and from water is critical to the function of water in many settings. However, it has been challenging to model. Here, we present proof-of-principle for an efficient yet robust model based on Lewis-inspired submolecular particles with interactions that deviate from Coulombic at short distances to take quantum effects into account. This "LEWIS" model provides excellent correspondence with experimental structures for water molecules and water clusters in their neutral, protonated and deprotonated forms, reasonable values for the proton affinities of water and hydroxide, a good value for the strength of the hydrogen bond in the water dimer, the correct order of magnitude for the stretch and bend force constants of water, and the expected time course for Grotthuss transport in water chains.

Natural polarizability and flexibility via explicit valency: The case of water

“…Also noteworthy in this category is the behavior of hexameric water clusters. An earlier parameterization of LEWIS, based on a strictly gas phase training set, 38 favored cage-like hexamers over ring-like ones, in agreement with high-level QM calculations. 75 On the other hand, the LEWIS parameters reported here do the opposite (see Table III).…”

“…38 Our approach is related to that of Stillinger's central force model 39 and polarization model 90 in the sense that carefully designed pairwise potentials allow full dissociability. However, we obviate extra polarization constructs by taking explicit account of valency.…”

“…Specifically, we unpack each water molecule into a +6e charged core (i.e., the combination of a +8e oxygen nucleus and a -2e pair of 1s electrons) surrounded by four −2e charged valence electron pairs and two protons bearing +1e charges. 38 These LEWIS particles are all independently mobile and represented by point locations that give the electron pairs a pseudo-classical nature. For efficiency, interactions are pairwise only.…”

Pointillist rendering of electron charge and spin density suffices to replicate trends in atomic properties

“…Optimism regarding kernel-kernel potentials is supported by the effectiveness of the kernel-kernel potentials developed in the earlier LEWIS model of water [28,29] which allowed for an excellent description of the solvation and dynamics of proton defects in bulk water [30]. Limitations of that construct were its modelling of the valence electrons in pairs with a fixed cloud radius.…”

Transferable pseudoclassical electrons for aufbau of atomic ions

“…While a heuristic approach to force fields is time consuming, it has the chance of providing a better set of potentials. The LEWIS force field takes this tack and also simplifies the problem by making only the valence electrons explicit and modeling them in pairs. For water, LEWIS provides an excellent description of cluster structures, the condensed phase, and proton defect solvation and dynamics .…”