For a century now, “Lewis dots” have been a mainstay of chemical thinking, teaching and communication. However, chemists have assumed that this semi-classical picture of electrons needs to be abandoned for quantitative work, and the recourse in computational simulations has been to the extremes of first principles treatments of electrons on the one hand and force fields that avoid explicit electrons on the other hand. Given both the successes and limitations of these highly divergent approaches, it seems worth considering whether the Lewis dot picture might be made quantitative after all. Here we review some of our progress toward that goal, including variations that have been developed and illustrative applications to acid-base chemistry in liquids. For water, our LEWIS force field competes favorably with DFT/GGA descriptions, predicting polarizability closer to MP2 values,1 hydration of the proton hole mirroring that of the excess proton,2 negative surface charge consistent with experiment,3 and dynamics that accord with experiment (including the diffusion coefficient of the proton hole relative to water and the excess proton,2 expected contributions to high frequency electrodynamics,4 the rate and path of self-ion recombination,4 and the pressure sensitivity of auto-ionization4). For the acid-catalyzed dehydration of methanol in the neat liquid, the semi-classical approach efficiently generates reasonable and readily interpreted reaction trajectories in turnkey fashion (i.e., without any input about products). Avenues for further progress are also discussed.5

Chemistry with semi-classical electrons: Reaction trajectories auto-generated by sub-atomistic force fields

254th National Meeting (2017)

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