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

Abstract

As the dominant physiological solvent, water drives the folding of biological macromolecules, influences conformational changes, determines the ionization states of surface groups, actively participates in catalytic events, and provides "wires" for long-range proton transfer. Elucidation of all these roles calls for atomistic simulations. However, currently available methods do not lend themselves to efficient simulation of proton transfer events, or even polarizability and flexibility. Here, we report that an explicit account of valency can provide a unified description for the polarizability, flexibility, and dissociability of water in one intuitive and efficient setting. We call this approach LEWIS, after the chemical theory that inspires the use of valence electron pairs. In this paper, we provide details of the method, the choice of the training set, and predictions for the neat ambient liquid, with emphasis on structure, dynamics, and polarization. LEWIS water provides a good description of bulk properties, and dipolar and quadrupolar responses.

Proton Defect Solvation and Dynamics in Aqueous Acid and Base

“…During 10 ns, the proton hole migrated with a diffusion constant, D OH− =0.15 Å 2 ps −1 ( Figure S2), which is intermediate between the 0.24 Å 2 ps −1 predicted for the excess proton and the 0.11 Å 2 ps −1 predicted for water. [14] This trend (D H3O+ > D OH-> D H2O ) agrees with the notion that proton transfer barriers are lower in acidic solutions than in basic ones. [6,22] As illustrated in Figure 2, the predicted ratio D OH-/D H3O+ =0.15/0.24=0.63 is reasonably close to the experimental ratio of 0.72.…”

“…[13] The mobile electron pairs allow bond formation and breaking, in addition to natural, multidimensional polarizability with the correct geometric response. [14] Thus LEWIS water is both dissociable as in Central Force Model [15] and polarizable and flexible as in TTM2-F. [16] The training of the LEWIS force field includes intermolecular interactions in the form of neutral, protonated and deprotonated water dimers. Of particular interest in the present context is the proton hopping barrier in the deprotonated dimer which is well reproduced by LEWIS, as shown in Figure S1.…”

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 .…”