Showing papers by "Peter T. Cummings published in 2020"

Critical Role of Anion–Solvent Interactions for Dynamics of Solvent-in-Salt Solutions

Abstract: Most polar solvent molecules are unstable toward electrode materials used in Li-based batteries. Solid electrolytes and ionic liquids are far more stable, however, they have relatively low conducti...

MoSDeF, a Python Framework Enabling Large-Scale Computational Screening of Soft Matter: Application to Chemistry-Property Relationships in Lubricating Monolayer Films.

Abstract: We demonstrate how the recently developed Python-based Molecular Simulation and Design Framework (MoSDeF) can be used to perform molecular dynamics screening of functionalized monolayer films, focusing on tribological effectiveness. MoSDeF is an open-source package that allows for the programmatic construction and parametrization of soft matter systems and enables TRUE (transferable, reproducible, usable by others, and extensible) simulations. The MoSDeF-enabled screening identifies several film chemistries that simultaneously show low coefficients of friction and adhesion. We additionally develop a Python library that utilizes the RDKit cheminformatics library and the scikit-learn machine learning library that allows for the development of predictive models for the tribology of functionalized monolayer films and use this model to extract information on terminal group characteristics that most influence tribology, based on the screening data.

Towards Molecular Simulations that are Transparent, Reproducible, Usable By Others, and Extensible (TRUE)

Abstract: Systems composed of soft matter (e.g., liquids, polymers, foams, gels, colloids, and most biological materials) are ubiquitous in science and engineering, but molecular simulations of such systems pose particular computational challenges, requiring time and/or ensemble-averaged data to be collected over long simulation trajectories for property evaluation. Performing a molecular simulation of a soft matter system involves multiple steps, which have traditionally been performed by researchers in a "bespoke" fashion, resulting in many published soft matter simulations not being reproducible based on the information provided in the publications. To address the issue of reproducibility and to provide tools for computational screening, we have been developing the open-source Molecular Simulation and Design Framework (MoSDeF) software suite. In this paper, we propose a set of principles to create Transparent, Reproducible, Usable by others, and Extensible (TRUE) molecular simulations. MoSDeF facilitates the publication and dissemination of TRUE simulations by automating many of the critical steps in molecular simulation, thus enhancing their reproducibility. We provide several examples of TRUE molecular simulations: All of the steps involved in creating, running and extracting properties from the simulations are distributed on open-source platforms (within MoSDeF and on GitHub), thus meeting the definition of TRUE simulations.

Towards molecular simulations that are transparent, reproducible, usable by others, and extensible (TRUE)

Abstract: Systems composed of soft matter (e.g., liquids, polymers, foams, gels, colloids, and most biological materials) are ubiquitous in science and engineering, but molecular simulations of such systems pose particular computational challenges, requiring time and/or ensemble-averaged data to be collected over long simulation trajectories for property evaluation. Performing a molecular simulation of a soft matter system involves multiple steps, which have traditionally been performed by researchers in a "bespoke" fashion, resulting in many published soft matter simulations not being reproducible based on the information provided in the publications. To address the issue of reproducibility and to provide tools for computational screening, we have been developing the open-source Molecular Simulation and Design Framework (MoSDeF) software suite. In this paper, we propose a set of principles to create Transparent, Reproducible, Usable by others, and Extensible (TRUE) molecular simulations. MoSDeF facilitates the publication and dissemination of TRUE simulations by automating many of the critical steps in molecular simulation, thus enhancing their reproducibility. We provide several examples of TRUE molecular simulations: All of the steps involved in creating, running and extracting properties from the simulations are distributed on open-source platforms (within MoSDeF and on GitHub), thus meeting the definition of TRUE simulations.

Diffusivity and Structure of Room Temperature Ionic Liquid in Various Organic Solvents.

Abstract: Room-temperature ionic liquids (RTILs) hold promise for applications in electric double layer capacitors (EDLCs), owing to a much wider potential window, lower vapor pressure, and better thermal and chemical stabilities compared to conventional aqueous and organic electrolytes. However, because the low diffusivity of ions in neat RTILs negates the EDLCs' advantage of high power density, the ionic liquids are often used in mixture with organic solvents. In this study, we measured the diffusivity of cations and anions in RTIL, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) ([BMIM+][TFSI-]), mixed with 10 organic solvents, by using the pulsed-field gradient NMR method. The ion diffusivity was found to follow that of neat solvents and in most studied solvents showed an excellent agreement with the predicted values reported in the recent molecular dynamics (MD) study [Thompson, M. W.; J. Phys. Chem. B 2019, 123, 1340-1347]. In two solvents consisting of long-chain molecules, however, the MD simulations predictions slightly underestimated the ionic diffusivities. The degree of ion dissociation was also estimated for each solvent by comparing the ionic conductivity with the molar conductivity derived from the diffusion measurements. The degree of ion dissociation and the hydrodynamic radius of ions suggest that the ions are coordinated by ∼1 solvent molecule. The scarcity of solvent-ion interactions explains the fact that the diffusivity of ions in the mixture significantly depends on the viscosity of the solvent.

Integral equation theory for a mixture of spherical and patchy colloids: analytical description.

Abstract: An analytic theory for the structure and thermodynamics of two-component mixtures of patchy and spherical colloids is developed. The theory is based on an analytical solution of the multidensity Ornstein-Zernike equation supplemented by the associative Percus-Yevick closure relations. We derive closed-form analytic expressions for the partial structure factors and thermodynamic properties using the energy route for the model with arbitrary number of patches and any hard-sphere size ratio of the particles. To assess the accuracy of the theoretical predictions we compare them against existing and newly generated set of computer simulation data. In our numerical calculations we consider the model with equal hard-sphere sizes and one patch. Very good agreement between results of the theory and simulation for the pair correlation functions, excess internal energy and pressure is observed for almost all values of the system density, temperature and composition studied. Only in the region of low concentrations of spherical colloids the theoretical results become less accurate.

Addition of Chloroform in a Solvent-In-Salt Electrolyte: Outcomes in the Microscopic Dynamics in Bulk and Confinement

Abstract: Solvent-in-salt electrolytes (SISEs) are a promising alternative to the electrolytes currently used in commercial devices. Nevertheless, despite the SISEs’ advantages, their applications are not ye...

Effects of nitrogen atoms on the stability and reactivity of tricyclic boracarbenes by DFT

Abstract: Following our quest for novel carbenes, effects of substituting 1 to 5 nitrogen atoms on the stability and reactivity of singlet (s) and triplet (t) forms of 7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-carbylenes (1–20) are compared and contrasted, at B3LYP/aug-cc-pvtz level of theory. All species appear as ground state minima on their energy surface, for showing no negative force constant. Singlets (1s–20s) are ground states and more stable than their corresponding triplets (1t–20t). Reactivity of the species (1s–20s vs. 1t–20t) is discussed in terms of isodesmic reactions, considering nucleophilicity (N), electrophilicity (ω), and heat of hydrogenation. As well as, the addition of nitrogen atoms decreased nucleophilicity (N), while increasing electrophilicity (ω). Despite the enormous steric strain involved in their cubic structures, the most stable scrutinized carbenes appear to be singlet 1,4,5-triaza-7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-carbylene (13) for showing the highest value of ΔEs–t. Such higher stabilization is attributed to a coordinate covalent bond observed between the carbenic center and the boron atom. This study offers new insights into the chemistry of these exotic tricyclic shaped carbenes.

Critical Role of Anion–Solvent Interactions for Dynamics of Solvent-in-Salt Solutions

Abstract: Most polar solvent molecules are unstable toward electrode materials used in Li-based batteries. Solid electrolytes and ionic liquids are far more stable; however, they have relatively low conductivity, and therefore electrical energy storage devices based on them would suffer from low power. Solvent-in-salt (SIS) systems combine chemical stability with relatively high conductivity. Here, we show how the nature of the employed anion affects the structure and dynamics of SIS systems. The transport of ions in lithium bis(fluorosulfonyl)imide (Li-FSI) systems was determined to be always faster than that in lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) systems. Moreover, we found that viscosity does not solely control conductivity and that the lower conductivity of TFSI– solutions is related to their stronger interaction with the solvent. This restricts solvent dynamics and slows down ion motions compared to that of FSI–. Interestingly, the TFSI–solvent interaction also leads to better charge separation (weaker ion–ion correlations) and a higher transference number for Li. Our results suggest that the ability to tune the solvent network formed around the anions may further improve electrolyte conductivity and Li transference number for safer and more efficient energy storage devices.