Proper treatment of nonbonded interactions is essential for the accuracy of molecular dynamics (MD) simulations, especially in studies of lipid bilayers. The use of the CHARMM36 force field (C36 FF) in different MD simulation programs can result in disagreements with published simulations performed with CHARMM due to differences in the protocols used to treat the long-range and 1-4 nonbonded interactions. In this study, we systematically test the use of the C36 lipid FF in NAMD, GROMACS, AMBER, OpenMM, and CHARMM/OpenMM. A wide range of Lennard-Jones (LJ) cutoff schemes and integrator algorithms were tested to find the optimal simulation protocol to best match bilayer properties of six lipids with varying acyl chain saturation and head groups. MD simulations of a 1,2-dipalmitoyl-sn-phosphatidylcholine (DPPC) bilayer were used to obtain the optimal protocol for each program. MD simulations with all programs were found to reasonably match the DPPC bilayer properties (surface area per lipid, chain order parameters, and area compressibility modulus) obtained using the standard protocol used in CHARMM as well as from experiments. The optimal simulation protocol was then applied to the other five lipid simulations and resulted in excellent agreement between results from most simulation programs as well as with experimental data. AMBER compared least favorably with the expected membrane properties, which appears to be due to its use of the hard-truncation in the LJ potential versus a force-based switching function used to smooth the LJ potential as it approaches the cutoff distance. The optimal simulation protocol for each program has been implemented in CHARMM-GUI. This protocol is expected to be applicable to the remainder of the additive C36 FF including the proteins, nucleic acids, carbohydrates, and small molecules.

CHARMM-GUI Membrane Builder, http://www.charmm-gui.org/input/membrane, is a web-based user interface designed to interactively build all-atom protein/membrane or membrane-only systems for molecular dynamics simulation through an automated optimized process. In this work, we describe the new features and major improvements in Membrane Builderthat allow users to robustly build realistic biological membrane systems, including (1) addition of new lipid types such as phosphoinositides, cardiolipin, sphingolipids, bacterial lipids, and ergosterol, yielding more than 180 lipid types, (2) enhanced building procedure for lipid packing around protein, (3) reliable algorithm to detect lipid tail penetration to ring structures and protein surface, (4) distance-based algorithm for faster initial ion displacement, (5) CHARMM inputs for P21 image transformation, and (6) NAMD equilibration and production inputs. The robustness of these new features is illustrated by building and simulating a membrane model of the polar and septal regions of E. coli membrane, which contains five lipid types: cardiolipin lipids with two types of acyl chains and phosphatidylethanolamine lipids with three types of acyl chains. It is our hope that CHARMM-GUI Membrane Builder becomes a useful tool for simulation studies to better understand the structure and dynamics of proteins and lipids in realistic biological membrane environments.

A passivation layer called the solid electrolyte interphase (SEI) is formed on electrode surfaces from decomposition products of electrolytes. The SEI allows Li + transport and blocks electrons in order to prevent further electrolyte decomposition and ensure continued electrochemical reactions. The formation and growth mechanism of the nanometer thick SEI films are yet to be completely understood owing to their complex structure and lack of reliable in situ experimental techniques. Significant advances in computational methods have made it possible to predictively model the fundamentals of SEI. This review aims to give an overview of state-of-the-art modeling progress in the investigation of SEI films on the anodes, ranging from electronic structure calculations to mesoscale modeling, covering the thermodynamics and kinetics of electrolyte reduction reactions, SEI formation, modification through electrolyte design, correlation of SEI properties with battery performance, and the artificial SEI design. Multiscale simulations have been summarized and compared with each other as well as with experiments. Computational details of the fundamental properties of SEI, such as electron tunneling, Li-ion transport, chemical/mechanical stability of the bulk SEI and electrode/(SEI/) electrolyte interfaces have been discussed. This review shows the potential of computational approaches in the deconvolution of SEI properties and design of artificial SEI. We believe that computational modeling can be integrated with experiments to complement each other and lead to a better understanding of the complex SEI for the development of a highly efficient battery in the future.

Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS2), recently discovered unexpected properties of WTe2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that bulk MoTe2 exhibits superconductivity with a transition temperature of 0.10 K. Application of external pressure dramatically enhances the transition temperature up to maximum value of 8.2 K at 11.7 GPa. The observed dome-shaped superconductivity phase diagram provides insights into the interplay between superconductivity and topological physics.

The mechanism of Li(+) transport through the solid electrolyte interphase (SEI), a passivating film on electrode surfaces, has never been clearly elucidated despite its overwhelming importance to Li-ion battery operation and lifetime. The present paper develops a multiscale theoretical methodology to reveal the mechanism of Li(+) transport in a SEI film. The methodology incorporates the boundary conditions of the first direct diffusion measurements on a model SEI consisting of porous (outer) organic and dense (inner) inorganic layers (similar to typical SEI films). New experimental evidence confirms that the inner layer in the ∼20 nm thick model SEI is primarily crystalline Li(2)CO(3). Using density functional theory, we first determined that the dominant diffusion carrier in Li(2)CO(3) below the voltage range of SEI formation is excess interstitial Li(+). This diffuses via a knock-off mechanism to maintain higher O-coordination, rather than direct-hopping through empty spaces in the Li(2)CO(3) lattice. Mesoscale diffusion equations were then formulated upon a new two-layer/two-mechanism model: pore diffusion in the outer layer and knock-off diffusion in the inner layer. This diffusion model predicted the unusual isotope ratio (6)Li(+)/(7)Li(+) profile measured by TOF-SIMS, which increases from the SEI/electrolyte surface and peaks at a depth of 5 nm, and then gradually decreases within the dense layer. With no fitting parameters, our approach is applicable to model general transport properties, such as ionic conductivity, for SEI films on the surface of other electrodes, from the atomic scale to the mesoscale, as well as aging phenomenon.

Solid-electrolyte interphase (SEI) is the key component that enables all advanced electrochemical devices, the best representative of which is Li-ion battery (LIB). It kinetically stabilizes electrolytes at potentials far beyond their thermodynamic stability limits, so that cell reactions could proceed reversibly. Its ad hoc chemistry and formation mechanism has been a topic under intensive investigation since the first commercialization of LIB 25 years ago. Traditionally SEI can only be formed in nonaqueous electrolytes. However, recent efforts successfully transplanted this concept into aqueous media, leading to significant expansion in the electrochemical stability window of aqueous electrolytes from 1.23 V to beyond 4.0 V. This not only made it possible to construct a series of high voltage/energy density aqueous LIBs with unprecedented safety, but also brought high flexibility and even "open configurations" that have been hitherto unavailable for any LIB chemistries. While this new class of aqueous electrolytes has been successfully demonstrated to support diversified battery chemistries, the chemistry and formation mechanism of the key component, an aqueous SEI, has remained virtually unknown. In this work, combining various spectroscopic, electrochemical and computational techniques, we rigorously examined this new interphase, and comprehensively characterized its chemical composition, microstructure and stability in battery environment. A dynamic picture obtained reveals how a dense and protective interphase forms on anode surface under competitive decompositions of salt anion, dissolved ambient gases and water molecule. By establishing basic laws governing the successful formation of an aqueous SEI, the in-depth understanding presented in this work will assist the efforts in tailor-designing better interphases that enable more energetic chemistries operating farther away from equilibria in aqueous media.

High-energy nickel (Ni)–rich cathode will play a key role in advanced lithium (Li)–ion batteries, but it suffers from moisture sensitivity, side reactions, and gas generation. Single-crystalline Ni-rich cathode has a great potential to address the challenges present in its polycrystalline counterpart by reducing phase boundaries and materials surfaces. However, synthesis of high-performance single-crystalline Ni-rich cathode is very challenging, notwithstanding a fundamental linkage between overpotential, microstructure, and electrochemical behaviors in single-crystalline Ni-rich cathodes. We observe reversible planar gliding and microcracking along the (003) plane in a single-crystalline Ni-rich cathode. The reversible formation of microstructure defects is correlated with the localized stresses induced by a concentration gradient of Li atoms in the lattice, providing clues to mitigate particle fracture from synthesis modifications.

Iodine-terminated self-assembled monolayer (I-SAM) was used in perovskite solar cells (PSCs) to achieve a 50% increase of adhesion toughness at the interface between the electron transport layer (ETL) and the halide perovskite thin film to enhance mechanical reliability. Treatment with I-SAM also increased the power conversion efficiency from 20.2% to 21.4%, reduced hysteresis, and improved operational stability with a projected T80 (time to 80% initial efficiency retained) increasing from ~700 hours to 4000 hours under 1-sun illumination and with continuous maximum power point tracking. Operational stability–tested PSC without SAMs revealed extensive irreversible morphological degradation at the ETL/perovskite interface, including voids formation and delamination, whereas PSCs with I-SAM exhibited minimal damage accumulation. This difference was attributed to a combination of a decrease in hydroxyl groups at the interface and the higher interfacial toughness.