We have studied how ReaxFF and Behler–Parrinello neural network (BPNN) atomistic potentials should be trained to be accurate and tractable across multiple structural regimes of Au as a representative example of a single‐component material. We trained these potentials using subsets of 9,972 Kohn‐Sham density functional theory calculations and then validated their predictions against the untrained data. Our best ReaxFF potential was trained from 848 data points and could reliably predict surface and bulk data; however, it was substantially less accurate for molecular clusters of 126 atoms or fewer. Training the ReaxFF potential to more data also resulted in overfitting and lower accuracy. In contrast, BPNN could be fit to 9,734 calculations, and this potential performed comparably or better than ReaxFF across all regimes. However, the BPNN potential in this implementation brings significantly higher computational cost. © 2016 Wiley Periodicals, Inc.
Molecular-level understanding and characterization of solvation environments are often needed across chemistry, biology, and engineering. Toward practical modeling of local solvation effects of any solute in any solvent, we report a static and all-quantum mechanics-based cluster-continuum approach for calculating single-ion solvation free energies. This approach uses a global optimization procedure to identify low-energy molecular clusters with different numbers of explicit solvent molecules and then employs the smooth overlap for atomic positions learning kernel to quantify the similarity between different low-energy solute environments. From these data, we use sketch maps, a nonlinear dimensionality reduction algorithm, to obtain a two-dimensional visual representation of the similarity between solute environments in differently sized microsolvated clusters. After testing this approach on different ions having charges 2+, 1+, 1−, and 2−, we find that the solvation environment around each ion can be seen to usually become more similar in hand with its calculated single-ion solvation free energy. Without needing either dynamics simulations or an a priori knowledge of local solvation structure of the ions, this approach can be used to calculate solvation free energies within 5% of experimental measurements for most cases, and it should be transferable for the study of other systems where dynamics simulations are not easily carried out.
Studies utilizing continuum solvation methods can sometimes omit critically important solute-solvent interactions, while explicitly sampling full solution phase mechanisms accurately with Born-Oppenheimer molecular dynamics (BOMD) is computationally costly. In this work, we benchmark components for an alternative IRCMax-like procedure for refined analyses of electronic energies along reaction pathways. The procedure involves obtaining molecular clusters from nudged elastic band calculations for use in mixed explicit-continuum models. The reaction energetics from these models correspond well to energetics obtained from explicit models using periodic boundary conditions, and the clusters obtained are more amenable to treatments with high levels of quantum chemistry theory. We demonstrate this approach using CO reduction by NaBH and NaBHOH in aqueous solution as test cases. We show that the local solvation environment containing explicit solvent molecules and a counterion within the entire first solvation shell significantly influences reaction energies. For the hydride transfers reported herein, the level of quantum chemistry theory used beyond that treated by standard GGA exchange correlation functionals normally plays a less significant role.
Electrode−electrolyte interfaces (EEIs) affect the rate capability, cycling stability, and thermal safety of lithium-ion batteries (LIBs). Designing stable EEIs with fast Li + transport is crucial for developing advanced LIBs. Here, we study Li + kinetics at EEIs tailored by three nanoscale polymer thin films via chemical vapor deposition (CVD) polymerization. Small binding energy with Li + and the presence of sufficient binding sites for Li + allow poly(3,4-ethylenedioxythiophene) (PEDOT) based artificial coatings to enable fast charging of LiCoO 2 . Operando synchrotron X-ray diffraction experiments suggest that the superior Li + transport property in PEDOT further improves current homogeneity in the LiCoO 2 electrode during cycling. PEDOT also forms chemical bonds with LiCoO 2 , which reduces Co dissolution and inhibits electrolyte decomposition. As a result, the LiCoO 2 4.5 V cycle life tested at C/2 increases over 1700% after PEDOT coating. In comparison, the other two polymer coatings show undesirable effects on LiCoO 2 performance. These insights provide us with rules for selecting/designing polymers to engineer EEIs in advanced LIBs.
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