We propose a first-principles atomistic method based on density functional theory and the non-equilibrium Green’s-function method to investigate the electronic and structural response of metal-insulator-metal capacitors under applied bias voltages. We validate our method by showing its usefulness in two paradigmatic cases where including finite-bias structural relaxation effects is critical to describe the device behavior: formation of dielectric dead layers in a paraelectric SRO|STO|SRO capacitor due to an applied bias voltage, and the switching behavior of a ferroelectric SRO|BTO|SRO capacitor due to an external electric field.

QuantumATK is an integrated set of atomic-scale modelling tools developed since 2003 by professional software engineers in collaboration with academic researchers. While different aspects and individual modules of the platform have been previously presented, the purpose of this paper is to give a general overview of the platform. The QuantumATK simulation engines enable electronic-structure calculations using density functional theory or tight-binding model Hamiltonians, and also offers bonded or reactive empirical force fields in many different parametrizations. Density functional theory is implemented using either a plane-wave basis or expansion of electronic states in a linear combination of atomic orbitals. The platform includes a long list of advanced modules, including Green's-function methods for electron transport simulations and surface calculations, first-principles electron-phonon and electron-photon couplings, simulation of atomic-scale heat transport, ion dynamics, spintronics, optical properties of materials, static polarization, and more. Seamless integration of the different simulation engines into a common platform allows for easy combination of different simulation methods into complex workflows. Besides giving a general overview and presenting a number of implementation details not previously published, we also present four different application examples. These are calculations of the phonon-limited mobility of Cu, Ag and Au, electron transport in a gated 2D device, multi-model simulation of lithium ion drift through a battery cathode in an external electric field, and electronic-structure calculations of the composition-dependent band gap of SiGe alloys.

We propose a new methodology called "one probe and non-equilibrium surface Green's function (OPNS)" to elucidate the longstanding controversial issue of a catalytic reaction mechanism, especially iodine reduction reaction (IRR) mechanisms. With aid of OPNS overcoming the limitations of conventional approach based on the free energy diagram and theoretical slab model, we clearly elucidate that the IRR follows a consecutive mechanism where the configurational preference of approaching I-2 molecules depending on the external electric field governs the IRR mechanism. Under reductive potential, I-2 molecules prefer a vertical configuration (I2V) rather than a parallel configuration (I2P), which leads to the consecutive mechanism where I atoms are sequentially reduced due to asymmetric charge accumulation on a single I atom that is subsequently desorbed. In addition, we provide new convincing descriptors for catalytic activity evaluation, the slope of the linear relation between the reductive process and the electric field strength representing the ability of the partial reduction and the threshold electric field of minimum required potential for the complete reduction.

We study from first principles the electrical characteristics of contacts between molybdenum ditelluride (MoTe2) and gold (Au), to understand the properties of closely related phase-engineered contacts, recently fabricated experimentally. In agreement with recent experiments, we find that while the Au|1 T'-MeTe2contact is Ohmic, the Au|2H-MoTe2contact exhibits a distinct Schottky-like behavior. These results suggest that the van der Waals gap at the Au|1 T'-MoTe2interface has a negligible impact on the electrical characteristics of these phase-engineered devices.

We present an efficient implementation of a surface Green's-function method for atomistic modeling of surfaces within the framework of density functional theory using a pseudopotential localized basis set approach. In this method, the system is described as a truly semi-infinite solid with a surface region coupled to an electron reservoir, thereby overcoming several fundamental drawbacks of the traditional slab approach. The versatility of the method is demonstrated with several applications to surface physics and chemistry problems that are inherently difficult to address properly with the slab method, including metal work function calculations, band alignment in thin-film semiconductor heterostructures, surface states in metals and topological insulators, and surfaces in external electrical fields. Results obtained with the surface Green's-function method are compared to experimental measurements and slab calculations to demonstrate the accuracy of the approach.

This is the study about the cathode's solid electrolyte interface (SEI) formation mechanism of salt type additives (STAB) and its function. To address this issue, we performed several types of chemical analysis and computer simulation techniques. In order to reveal the redox nature and oxidative decomposition dynamics, the electrolyte (EL) solution dynamics by Quantum mechanics and Molecular mechanics (QM/MM) method was applied. The estimation of SEI chemical components agrees with our chemical analyses data and other group's reports. The molecular dynamics simulation of sub micro second sampling indicates that the SEI phase induced from STAB functions as a lithium ion selective translocation media and protective coating layer against the degradation of the solvent molecules. The results give us an insight how to design additive's chemical structure to improve longevity of the cell in the high voltage regime. (C) 2016 Elsevier Ltd. All rights reserved.

The effect of additives in an electrolyte solution on the conversion efficiency of a dye sensitized solar cell was investigated. A density functional theory (DFT) method was used to examine the physical and chemical properties of nitrogen-containing additives adsorbed on a TiO2 surface. Our results show that additives which cause lower partial charges, higher Fermi level shifts, and greater adsorption energies tend to improve the performance of DSSCs. Steric effects that prevent energy losses due to electron recombination were also found to have a positive effect on the conversion efficiency. In this work, 3-amino-5-methylthio-1H-1,2,4-triazole (AMT) has been suggested as a better additive than the most popular additive, TBP, and verified with experiments.

Solid state lithium oxide compounds of layered structure, which has high stability of structure, are mainly used as the cathode materials in lithium-ion batteries (LIBs). Recently, the investigation of Solid Electrolyte Interphase (SEI) between active materials and electrolyte has been focusing to improve the performance of lithium-ion batteries. For the investigation of the SEI, the study of surface properties of cathode materials and anode materials is also required in advance. LiNiO2 and LiCoO2 are very similar layered structure of cathode active materials and representative solid state lithium oxide compounds in LIBs. Various experimental and theoretical studies have been doing for LiCoO2. The theoretical investigation of LiNiO2 is not sufficient, however, even if experimental studies of LiNiO2 are enough. In this study, the surface energies of nine facets of LiNiO2 crystal facets were calculated by Density Functional Theory. In XRD data of LiNiO2, (003), (104), (101), et al. facets are main surfaces in order. However, the results of calculation are different with XRD data. Thus, both (104) and (101) facets, which are energetically stable and measured in XRD, are mainly exposed in the surface of LiNiO2 and it is expected that intercalation and de-intercalation of Li- ion will be affected by them.

As the development of available binder in the harsh conditions is needed, we propose the proper binder for high-voltage lithium-ion secondary batteries based on the quantum chemistry modeling. The optimized structures, HOMO (Highest Occupied Molecular Orbital) energies and ionization potentials of 4 binders, which were considered from monomer to tetramer, were investigated by the semi-empirical and DFT (Density Functional Theory) calculations. The results show that the ionization potential values by calculation tend to be close to the oxidation potentials from the measurement of linear sweep voltametry (LSV). The order of oxidative resistance from high value to low value is following: poly(hexafluropropylene), poly(vinylidene fluoride), poly(methyl acrylate) and poly(acryl amide). Also these results correspond with the experimental values. Thus, we find the reason why HOMO (Highest Occupied Molecular Orbital) energy of PHFP has the highest value than other binders by analysis of HOMO orbital structures.

The adhesion strengths between LiFePO4 cathodes and aluminum (Al) current collectors as well as the corresponding electrochemical properties of electrodes with carboxylated poly(vinyl difluoride) (C-PVdF) were experimentally and theoretically investigated. The adhesion strength of LiFePO4 cathodes with C-PVdF on Al current collectors were increased, compared with that of as received PVdF, resulting in the reduction of the internal resistance of the electrode. These results were supported by theoretical simulations based on the Metropolis Monte Carlo method. Electrochemical experiments indicated that the cyclability and rate capabilities of the cathode were improved as the weight fraction of C-PVdF in the electrode increased up to 70% of the polymer binders. In addition, 18 650-sized full cells employing the electrodes with C-PVdF showed promising performance in terms of rate capability as well as long-term cyclability, which suggests that this strategy can be beneficial for the realization of high power sources such as electric Vehicle's, electric bikes, and various power tools.

The adhesion strength of the electrode on the current collector in lithium-ion rechargeable batteries (LIBs) is a dominant factor determining the long-term cycle life of LIBs, which is significantly affected by the physicochemical properties of binder in the electrode. In this paper, we have theoretically and experimentally investigated improvement in the adhesion strength of the LiFePO4 (LFP) positive electrode on the aluminum current collector and the corresponding electrochemical behavior of the LIBs through controlling the functional groups in poly(vinyldifluoride)s (PVdFs) acting as a binder in the electrode. Based on the Metropolis Monte Carlo method, the theoretical simulation was performed to explore the binding energy of the functional group in PVdF on (100) plane of aluminum surface terminated with oxygen and hydrogen. It was found that the carboxylic group in PVdF provides the highest binding energy with aluminum in comparison to the other functional groups, which implies that it can impart the strongest adhesion strength between the positive electrode and the current collector (Table I). This theoretical analysis was in good agreement with the experimental results. The LFP/carbon black suspensions were prepared with PVdF and carboxylated PVdF, respectively. As shown in Table II, the adhesion strength of the positive electrode with the carboxylated PVdF was ~3gf/mm, which was a factor of approximately 3 higher than that with the as-received PVdF. Correlation was made between the adhesion strength of LFP electrode on aluminum current collector and the electrochemical behaviors of LIBs fabricated in the form of the cylindrical 18650-sized full cells (Fig. 1). The electrochemical experiments indicated that the carboxylated PVdF led to improved cycle life, showing a discharge capacity exceeding 90% of the initial discharge capacity after 200th cycles. This study is expected to impact the realization the super hugecapacity batteries (>50Ah/cell).

Structural aspects of terminally blocked alanine trans-N-acetyl-L-alanyl-trans-/N'-methylamide (Ac-Ala-NHMe) in several different solvents were compared by attenuated total reflection infrared (ATR-IR) spectroscopy and density functional theory (DFT) calculations. The amide I bands between 1600 and 1700 cm(-1) appeared to change depending on media, indicating dissimilar hydrogen-bonding interactions among the peptides and solvent molecules. The minimum energy geometry in the isolated gas phase and aqueous environments were calculated at the B3LYP/6-311++G** theoretical level. In the solid state, Ac-Ala-NHMe is assumed to have an extended beta-stranded structure (C-5); whereas it is assumed to have a cyclic structure (C7(eq) or alpha(L)) in a nonpolar tetrahydrofuran (THF) solvent. The optimized backbone dihedral angles (Phi, Psi) of Ac-Ala-NHMe plus four explicit water molecules were estimated to be -94 degrees and +133 degrees, respectively, indicating the polyproline II structure (P-II). The energy differences between the most stable conformers were predicted to be larger for Ac-Ala-NHMe, which implies that more conformational ensemble structures should coexist for the gas phase than for the aqueous medium with explicit water molecules.

We studied solvation structure and thermodynamics of methane in mixtures of tert-butanol and water using computer simulations. We show that for alcohol mole fractions below 20%, methane is preferentially solvated by hydrated alcohol clusters. Because methane expels water molecules from these clusters, a large endothermic solvent reorganization enthalpy occurs. This process is responsible for the experimentally observed maximum of the heat of methane solvation close to 5% alcohol in the mixture and contributes to a positive entropy change relative to solvation in pure water. Because the structural solvent reorganization enthalpy is enthalpy-entropy compensating, the methane solvation free energy is a smoothly varying function of the alcohol/water solution composition.

By comparison of neopentane pair potentials of mean force (PMFs) in room temperature water and 6.9 molar aqueous urea, it was recently shown that urea molecules affect the PMF minima in an unexpected way (Lee, M.-E.; van der Vegt, N. F. A. J. Am. Chem. Soc. 2006, 128, 4948). While the first PMF minimum in urea solution has an identical shape and depth to those of the corresponding minimum in water, the second minimum in urea solution is broader, deeper, and shifted out to a slightly larger distance. Here, we present a study of the enthalpic and entropic contributions to these PMFs. Its significance for understanding the driving forces responsible for thermodynamically favorable neopentane contact and solvent-separated distances in urea solution is discussed. We propose that the solute-solvent entropy and solute-solvent enthalpy changes should be analyzed for obtaining an unambiguous molecular-scale picture. In urea solution, enthalpy-entropy compensation effects associated with structural solvent reorganization processes are large, causing changes of the system's enthalpy and entropy with hydrophobic pair separation to be very different from the solute-solvent enthalpy and entropy changes. The entropies are discussed in terms of the molecular-scale solvent reorganization processes.