No abstract

Quantum-Guided Molecular Mechanics (Q2MM) can be used to derive transition state force fields (TSFFs) that allow the fast and accurate predictions of stereoselectivity for a wide range of catalytic enantioselective reactions. The basic ideas behind the derivation of TSFFs using Q2MM are discussed and the steps involved in obtaining a TSFF using the Q2MM code, publically available at github.com/q2mm, are shown. The applicability for a range of reactions, including several non-standard applications of Q2MM, is demonstrated. Future developments of the method are also discussed.

The optimal salt concentration used in metal-ion energy storage devices has long focused heavily on 1 M electrolytes; however, recent evidence suggests taking a deeper look at electrolyte properties as a function of salt concentration. Toward that goal, the effect of concentration on solvation properties for a prototype sodium electrolyte is considered with potential applications for sodium-ion and sodium−air technologies. An empirical force field for sodium triflate in digylme, an electrolyte already in use with sodium−air systems, was developed from ab initio molecular dynamics simulations in conjunction with the variational force-matching method. Atomistic simulations of this electrolyte along with Fourier transform infrared (FTIR) experimental studies validate the qualitative accuracy of the model and demonstrate its transferability across different concentrations. The solvation structure and the extent of ion pairing effects in the electrolyte were considered for concentrations ranging from 0.25 to 2.0 M in the sodium salt. Ion pairing effects are seen even at dilute concentrations of 0.5 M in both simulations and experiments, with a transition from solvent-separated species to direct contact ion pairs as the concentration increased to 1.5 M. With further increase in the concentration, evidence for ion aggregation is also presented.