Toward Realistic Transfer Rates within the Coupled Molecular Dynamics/Lattice Monte Carlo Approach

Abstract

We refine our recently developed coupled molecular dynamics/lattice Monte Carlo (cMD/LMC) scheme for the simulation of protonation dynamics in complex hydrogen-bonded solids in view of improving the resulting transport processes. The distance dependency of the proton jump rate between lattice sites and its dependence on additional geometric criteria (bond angles) are derived in a systematic and consistent way. The distance dependency follows an accurate potential energy surface (PES) scan from quantum chemical calculations. The novel geometric criterion takes into account that proton hopping occurs almost exclusively along linear hydrogen bonds. We illustrate the capabilities and the versatility of our scheme on the example of two chemically quite different condensed phase systems: a crystalline solid acid compound and a liquid crystal. Surprisingly, we find that our cMD/LMC scheme yields converged mobility parameters even when based on underlying ab initio molecular dynamics (AIMD) trajectories which themselves are not fully converged. Our method yields more accurate values for the mean square displacement, the OH bond autocorrelation function and the proton jump frequencies in agreement with both reference AIMD simulations and experimental values.

Proton Conductivity in Hydrogen Phosphate/Sulfates from a Coupled Molecular Dynamics/Lattice Monte Carlo (cMD/LMC) Approach

“…Each Monte Carlo run was performed for the equivalent of 250 ps following the recently improved version of our cMD/LMC scheme . The heavy atom structure was updated in the continuous mode .…”

“…The heavy atom structure was updated in the continuous mode . An angular cut off criterion for the P–O–O and S–O–O angle of 90° was used for the proton jumps (for explanation see ref ). Before starting the production run, every MC simulation was equilibrated for 125 ps.…”

“…The algorithmic details of this combined cMD/LMC approach and its validation in terms of accuracy for the reference systems have been published elsewhere . In this work, we use a refined version of the cMD/LMC approach to explain the changes in proton conductivity in a series of solid acids, upon temperature variations, phase transitions, and chemical variations.…”

“… The ionic conductivity of solid acids of CsH n XO 4 type (X = P, S; n = 2, 1) varies upon chemical substitution P ↔ S and between different crystal structures (T c = 503 K for CsH 2 PO 4 ). We apply a recently developed coupled molecular dynamics/lattice Monte Carlo simulation approach (cMD/LMC , ) to explain both the phosphate/sulfate and temperature/phase-related variations of the proton conductivity on a molecular level. Our simulation method elucidates the relative importance of the two key components of the Grotthuss-type proton conduction mechanism, proton hopping and structural reorientation, as a function of the chemical/thermodynamical conditions.…”

Adduct under Field—A Qualitative Approach to Account for Solvent Effect on Hydrogen Bonding

“…Proton transfer represents the simplest possible chemical reaction [1] and is ubiquitous in chemistry [2,3], material science [4][5][6], and biology [7,8]. In the latter case, the complexity of the process can increase to a hydrogen atom transfer [9,10].…”