In non-self-consistent LDA-1/2 calculations, the resulting electron wave functions illustrate a more extreme and unacceptable localization, as a consequence of the Hamiltonian's disregard for the powerful Coulombic repulsion. One frequent flaw in non-self-consistent LDA-1/2 models is the substantial amplification of bonding ionicity, which can cause exceptionally high band gaps in mixed ionic-covalent materials, such as TiO2.
An in-depth analysis of electrolyte-reaction intermediate interactions and the promotion of reactions by electrolyte in electrocatalysis is a difficult endeavor. Theoretical calculations are employed to explore the reaction mechanism of CO2 reduction to CO on the Cu(111) surface, considering various electrolytes. Investigating the charge distribution during the chemisorption of CO2 (CO2-), we find electron transfer from the metal electrode to CO2. The hydrogen bonding interaction between electrolytes and CO2- significantly stabilizes the CO2- structure and lowers the formation energy of *COOH. The vibrational frequency signatures of intermediary species across different electrolyte solutions show water (H₂O) as a part of bicarbonate (HCO₃⁻), thus supporting carbon dioxide (CO₂) adsorption and reduction. Essential to comprehending interface electrochemistry reactions involving electrolyte solutions are the insights gleaned from our research, which also shed light on catalysis at a molecular scale.
The kinetics of formic acid dehydration on a polycrystalline platinum electrode, at pH 1, influenced by adsorbed CO (COad), were analyzed using time-resolved ATR-SEIRAS, coupled with simultaneous current transient measurements after a potential step. To achieve a deeper understanding of the reaction's mechanism, formic acid concentrations were systematically varied across a range of values. The rate of dehydration's potential dependence has been confirmed by experiments to exhibit a bell curve, peaking near zero total charge potential (PZTC) at the most active site. HOpic Analyzing the integrated intensity and frequency of COL and COB/M bands demonstrates a progressive accumulation of active sites on the surface. The observed relationship between COad formation rate and potential supports a mechanism involving the reversible electroadsorption of HCOOad, followed by its reduction to COad, which is the rate-determining step.
Self-consistent field (SCF) calculations are used to assess and compare methods for determining core-level ionization energies. A full core-hole (or SCF) approach accounting completely for orbital relaxation upon ionization is part of the set of methods. These methods also incorporate methods based on Slater's transition idea, wherein the binding energy is estimated from an orbital energy level established through a fractional-occupancy SCF procedure. Furthermore, a generalization utilizing two distinct fractional-occupancy self-consistent field approaches is taken into account. Among Slater-type methods, the best achieve mean errors of 0.3 to 0.4 eV compared to experimental K-shell ionization energies, a degree of accuracy on par with more expensive many-body calculations. An empirical adjustment procedure, contingent on a single variable, minimizes the average error to below 0.2 electron volts. This refined Slater transition method proves a simple and practical means of calculating core-level binding energies, utilizing solely the initial-state Kohn-Sham eigenvalues. This method, requiring no more computational resources than SCF, is particularly useful for simulating transient x-ray experiments. Within these experiments, core-level spectroscopy is utilized to investigate excited electronic states, a task that the SCF method addresses through a protracted series of state-by-state calculations of the spectrum. Illustrative of the modeling process, we utilize Slater-type methods for x-ray emission spectroscopy.
Layered double hydroxides (LDH), previously functioning as an alkaline supercapacitor material, can be electrochemically converted to a neutral-electrolyte-compatible metal-cation storage cathode. However, large cation storage efficiency is restricted by the limited interlayer separation within LDH. HOpic By substituting interlayer nitrate ions with 14-benzenedicarboxylic anions (BDC), the interlayer spacing of NiCo-LDH is broadened, resulting in improved rate capabilities for accommodating larger cations (Na+, Mg2+, and Zn2+), while exhibiting minimal change when storing smaller Li+ ions. The BDC-pillared layered double hydroxide (LDH-BDC)'s enhanced rate performance during charge/discharge arises from the decreased charge-transfer and Warburg resistances, as determined by in situ electrochemical impedance spectra, which correlate with an increase in the interlayer distance. Cycling stability and high energy density are observed in the asymmetric zinc-ion supercapacitor, a product of LDH-BDC and activated carbon materials. This investigation highlights a successful technique to bolster the large cation storage capability of LDH electrodes, accomplished by augmenting the interlayer distance.
Applications of ionic liquids as lubricants and as additives to conventional lubricants are driven by their unique physical properties. These liquid thin films, within these applications, experience extreme shear and load conditions concurrently, compounded by the effects of nanoconfinement. We scrutinize a nanometric ionic liquid film, confined between two planar, solid surfaces, through coarse-grained molecular dynamics simulations, examining its behavior under equilibrium and a range of shear rates. Through the simulation of three unique surfaces, each with heightened interactions with distinct ions, the strength of the interaction between the solid surface and the ions was altered. HOpic A solid-like layer, moving with the substrates, is created by the interaction of either the cation or the anion, but its structural characteristics and stability are prone to differentiation. A heightened interaction with the anion possessing high symmetry produces a more regular and robust structure, providing greater resistance to shear and viscous heating. Viscosity was determined using two definitions. The first relied upon the microscopic characteristics of the liquid, the second on forces measured at solid surfaces. This microscopic-based definition demonstrated a correlation with the layered structural patterns established by the surfaces. Increasing shear rate leads to a reduction in both the engineering and local viscosities of ionic liquids, a consequence of their shear-thinning behavior and the temperature rise from viscous heating.
Computational methods, specifically classical molecular dynamics simulations using the Atomic Multipole Optimized Energetics for Biomolecular Simulation (AMOEBA) polarizable force field, were used to establish the vibrational spectrum of the alanine amino acid in the infrared range (1000-2000 cm-1) under varying environmental conditions, including gas, hydrated, and crystalline states. Spectra were effectively decomposed into various absorption bands, each associated with a unique internal mode, through a rigorous mode analysis. The gas-phase analysis process elucidates the significant distinctions between neutral and zwitterionic alanine spectral outputs. Within condensed phases, the approach provides insightful knowledge regarding the vibrational band's molecular origins, and conspicuously exhibits that peaks sharing similar positions can originate from rather diverse molecular activities.
A protein's response to pressure, resulting in shifts between its folded and unfolded forms, is a critical but not fully understood process. Water's behavior, impacting protein conformations, is directly influenced by pressure, as the critical factor. Molecular dynamics simulations, executed at 298 Kelvin, are employed here to systematically investigate how protein conformations correlate with water structures at pressures of 0.001, 5, 10, 15, and 20 kilobars, starting from the (partially) unfolded states of bovine pancreatic trypsin inhibitor (BPTI). Thermodynamic properties at those pressures are also calculated by us, in correlation with the protein's proximity to water molecules. Pressure's impact, as our research indicates, is characterized by effects that are both protein-targeted and more general in nature. Specifically, our analysis indicated that (1) water density near proteins increases depending on the protein's structural complexity; (2) pressure reduces intra-protein hydrogen bonds, but enhances water-water hydrogen bonds within the first solvation shell (FSS); protein-water hydrogen bonds correspondingly increase with pressure; (3) pressure induces a twisting effect on the water hydrogen bonds within the FSS; (4) the tetrahedrality of water within the FSS decreases with pressure, which is modulated by the local environment. Pressure-volume work is the principal thermodynamic driver for the structural perturbation of BPTI at higher pressures, whereas the entropy of water molecules within the FSS decreases due to their increased translational and rotational rigidity. The pressure-induced protein structure perturbation, which is typical, is expected to exhibit the local and subtle effects, as observed in this work.
Adsorption occurs when a solute concentrates at the interface between a solution and another gas, liquid, or solid phase. The macroscopic theory of adsorption, a theory with origins more than a century in the past, is now remarkably well-understood. Even with recent progress, a complete and self-contained theory for the phenomenon of single-particle adsorption has not been developed. We build a microscopic theory of adsorption kinetics to close this gap, and this theory yields macroscopic properties seamlessly. One of our most important achievements involves the microscopic manifestation of the Ward-Tordai relation. This relation's universal equation interconnects surface and subsurface adsorbate concentrations, applicable for all adsorption mechanisms. Moreover, we provide a microscopic interpretation of the Ward-Tordai relation, leading to its broader application encompassing arbitrary dimensions, geometries, and initial states.