Density functional study of CO and NO adsorption on Ni-doped MgO(100)

Accurate Force Fields for Atomistic Simulations of Oxides, Hydroxides, and Organic Hybrid Materials up to the Micrometer Scale

The simulation of metals, oxides, and hydroxides can accelerate the design of therapeutics, alloys, catalysts, cement-based materials, ceramics, bioinspired composites, and glasses. Here we introduce the INTERFACE force field (IFF) and surface models for α-Al2O3, α-Cr2O3, α-Fe2O3, NiO, CaO, MgO, β-Ca(OH)2, β-Mg(OH)2, and β-Ni(OH)2. The force field parameters are nonbonded, including atomic charges for Coulomb interactions, Lennard-Jones (LJ) potentials for van der Waals interactions with 12-6 and 9-6 options, and harmonic bond stretching for hydroxide ions. The models outperform DFT calculations and earlier atomistic models (Pedone, ReaxFF, UFF, CLAYFF) up to 2 orders of magnitude in reliability, compatibility, and interpretability due to a quantitative representation of chemical bonding consistent with other compounds across the periodic table and curated experimental data for validation. The IFF models exhibit average deviations of 0.2% in lattice parameters, <10% in surface energies (to the extent known), and 6% in bulk moduli relative to experiments. The parameters and models can be used with existing parameters for solvents, inorganic compounds, organic compounds, biomolecules, and polymers in IFF, CHARMM, CVFF, AMBER, OPLS-AA, PCFF, and COMPASS, to simulate bulk oxides, hydroxides, electrolyte interfaces, and multiphase, biological, and organic hybrid materials at length scales from atoms to micrometers. The nonbonded character of the models also enables the analysis of mixed oxides, glasses, and certain chemical reactions, and well-performing nonbonded models for silica phases, SiO2, are introduced. Automated model building is available in the CHARMM-GUI Nanomaterial Modeler. We illustrate applications of the models to predict the structure of mixed oxides, and energy barriers of ion migration, as well as binding energies of water and organic molecules in outstanding agreement with experimental data and calculations at the CCSD(T) level. Examples of model building for hydrated, pH-sensitive oxide surfaces to simulate solid-electrolyte interfaces are discussed.

Periodic Density Matrix Embedding for CO Adsorption on the MgO(001) Surface

The adsorption of simple gas molecules to metal oxide surfaces is a primary step in many heterogeneous catalysis applications. Quantum chemical modeling of these reactions is a challenge in terms of both cost and accuracy, and quantum-embedding methods are promising, especially for localized chemical phenomena. In this work, we employ density matrix embedding theory (DMET) for periodic systems to calculate the adsorption energy of CO to the MgO(001) surface. Using coupled-cluster theory with single and double excitations and second-order Møller-Plesset perturbation theory as quantum chemical solvers, we perform calculations with embedding clusters up to 266 electrons in 306 orbitals, with the largest embedding models agreeing to within 1.2 kcal/mol of the non-embedding references. Moreover, we present a memory-efficient procedure of storing and manipulating electron repulsion integrals in the embedding space within the framework of periodic DMET.

Magnesium oxide nanotube as a promising material for detection of methamphetamine drug: theoretical study

Owing to the negative impacts of abusing illegal drugs like methamphetamine (MAF), their detection and control are of paramount importance. Therefore, it is very critical to determine MAF in biological samples. The current research study investigated the sensing interaction of inherent and MgO nanotubes (MgONT) toward MAF via density functional theory computations. We determined that the MgONT has a sensing response of 283.31, and it remarkably improves the reactivity toward MAF. The levels of energy for the highest occupied and the lowest unoccupied molecular orbitals have changed to a great extent, thereby reducing bandgap (E_g) values which increased electrical conductivity. Furthermore, a short recovery time (~ 28.65 ms) has been anticipated for MAF desorption from the MgONT exterior. This piece of research showed that MgONT might be a possible electronic sensor and an appropriate choice to deliver MAF in biological samples.

How Accurate Are Approximate Density Functionals for Noncovalent Interaction of Very Large Molecular Systems?

Noncovalent intermolecular interactions are very important in many research areas. Therefore, it is vital to understand the extent to which approximate density functionals give a proper description of noncovalent interactions. Previous research has demonstrated that some approximate density functionals can predict usefully accurate interaction energies for many noncovalent systems; however, most of that work is limited to small and moderate-sized molecules. Very recently though, accurate benchmarks have become available for some very large molecules. The present work applies 21 approximate density functionals to compute the binding energies of seven large molecular systems that have a number of atoms ranging from 200 to 910. The results are judged by comparison to the recently published CIM-DLPNO-CCSD(T) results, which are assumed to provide a reliable benchmark. The five most accurate methods among those tested are found to be PW6B95-D4, PW6B95-D3(BJ), revM11, M06-L, and MN15.

S. Azevedo D, Guzmán-Vargas A, Felipe C. Effect of Calcination Temperature and Chemical Composition of PAN-Derived Carbon Microfibers on N2, CO2, and CH4 Adsorption

This work investigates the interplay of carbonization temperature and the chemical composition of carbon microfibers (CMFs), and their impact on the equilibration time and adsorption of three molecules (N₂, CO₂, and CH₄). PAN derived CMFs were synthesized by electrospinning and calcined at three distinct temperatures (600, 700 and 800 °C), which led to samples with different textural and chemical properties assessed by FTIR, TGA/DTA, XRD, Raman, TEM, XPS, and N₂ adsorption. We examine why samples calcined at low/moderate temperatures (600 and 700 °C) show an open hysteresis loop in nitrogen adsorption/desorption isotherms at -196.15 °C. The equilibrium time in adsorption measurements is nearly the same for these samples, despite their distinct chemical compositions. Increasing the equilibrium time did not allow for the closure of the hysteresis loop, but by rising the analysis temperature this was achieved. By means of the isosteric enthalpy of adsorption measurements and ab initio calculations, adsorbent/adsorbate interactions for CO₂, CH₄ and N₂ were found to be inversely proportional to the temperature of carbonization of the samples (CMF-600 > CMF-700 > CMF-800). The enhancement of adsorbent/adsorbate interaction at lower carbonization temperatures is directly related to the presence of nitrogen and oxygen functional groups on the surface of CMFs. Nonetheless, a higher concentration of heteroatoms also causes: (i) a reduction in the adsorption capacity of CO₂ and CH₄ and (ii) open hysteresis loops in N₂ adsorption at cryogenic temperatures. Therefore, the calcination of PAN derived microfibers at temperatures above 800 °C is recommended, which results in materials with suitable micropore volume and a low content of surface heteroatoms, leading to high CO₂ uptake while keeping acceptable selectivity with regards to CH₄ and moderate adsorption enthalpies.

Hydrogen bonding networks in gabapentin protic pharmaceutical salts: NMR and in silico studies

Hydrogen bonds (HBs) play a key role in the supramolecular arrangement of crystalline solids and, although they have been extensively studied, the influence of their strength and geometry on crystal packing remains poorly understood. Here we describe the crystal structures of two novel protic gabapentin (GBP) pharmaceutical salts prepared with the coformers methanesulfonic acid (GBP:METHA) and ethanesulfonic acid (GBP:ETHA). This study encompasses experimental and computational electronic structure analyses of ¹ H NMR chemical shifts (CSs), upon in silico HB cleavage. GBP:METHA and GBP:ETHA crystal packing comprise two main structural domains: an ionic layer (characterized by the presence of charge-assisted ⁺ NH_GBP ⋯O^-_METHA/ETHA HB interactions) and a neutral layer generated in a different way for each salt, mainly due to the presence of bifurcated HB interactions. A comprehensive study of HB networks is presented for GBP:METHA, by isolating molecular fragments involved in distinct HB types (NH⋯O, OH⋯O, and CH⋯O) obtained from in silico disassembling of an optimized three-dimensional packing structure. Formation of HB leads to calculated ¹ H NMR CS changes from 0.4 to ~5.8 ppm. This study further attempts to assess how ¹ H NMR CS of protons engaged in certain HB are affected when other nearby HB, involving bifurcated or geminal/vicinal hydrogen atoms, are removed.

A DFT study on the interaction of small molecules with alkali metal ion-exchanged ETS-10

In this paper, we present a systematic quantum-mechanical density functional theory (DFT) study of adsorption of small gas molecules in cation-exchanged Engelhard titanosilicate ETS-10 crystalline materials. Adsorbates with a range of polarities were considered, ranging from polar (H2O), quadrupolar (CO2 and N2), to apolar (CH4) atmospheric gases. Starting from the base-case of Na-ETS-10, other extra framework cations such as Li+, K+, Rb+ and Cs+ were considered. The DFT calculations were performed with the M06-L functional and were corrected for basis set superposition error with the counterpoise method in order to provide accurate and robust geometries and adsorption energies. For all adsorbates, the adsorption enthalpies decrease in the order Li+>Na+>K+>Rb+>Cs+, while adsorbate – cation interaction distances increase along the same order. For the two extreme cases, the enthalpies calculated at the M06-L/6-31++G** level of theory for CH4, N2, CO2, and H2O interaction with Li+(Cs+) exchanged materials are −21.8 (−1.7) kJ·mol−1, −19.0 (−10.7) kJ·mol−1, −34.4 (−21.3) kJ·mol−1, and −70.5 (−36.1) kJ·mol−1, respectively. Additionally, the calculated vibrational frequencies are found to be in quite good agreement with the characteristic vibrational modes of alkali metal cation-exchanged ETS-10 and also with the available experimental frequencies for CH4, N2, CO2, and H2O interactions with alkali metal cations in the 12-membered channel of ETS-10.

Computational Design of Functionalized Metal-Organic Framework Nodes for Catalysis

Recent progress in the synthesis and characterization of metal-organic frameworks (MOFs) has opened the door to an increasing number of possible catalytic applications. The great versatility of MOFs creates a large chemical space, whose thorough experimental examination becomes practically impossible. Therefore, computational modeling is a key tool to support, rationalize, and guide experimental efforts. In this outlook we survey the main methodologies employed to model MOFs for catalysis, and we review selected recent studies on the functionalization of their nodes. We pay special attention to catalytic applications involving natural gas conversion.

Simulations of inorganic-bioorganic interfaces to discover new materials: insights, comparisons to experiment, challenges, and opportunities

Natural and man-made materials often rely on functional interfaces between inorganic and organic compounds. Examples include skeletal tissues and biominerals, drug delivery systems, catalysts, sensors, separation media, energy conversion devices, and polymer nanocomposites. Current laboratory techniques are limited to monitor and manipulate assembly on the 1 to 100 nm scale, time-consuming, and costly. Computational methods have become increasingly reliable to understand materials assembly and performance. This review explores the merit of simulations in comparison to experiment at the 1 to 100 nm scale, including connections to smaller length scales of quantum mechanics and larger length scales of coarse-grain models. First, current simulation methods, advances in the understanding of chemical bonding, in the development of force fields, and in the development of chemically realistic models are described. Then, the recognition mechanisms of biomolecules on nanostructured metals, semimetals, oxides, phosphates, carbonates, sulfides, and other inorganic materials are explained, including extensive comparisons between modeling and laboratory measurements. Depending on the substrate, the role of soft epitaxial binding mechanisms, ion pairing, hydrogen bonds, hydrophobic interactions, and conformation effects is described. Applications of the knowledge from simulation to predict binding of ligands and drug molecules to the inorganic surfaces, crystal growth and shape development, catalyst performance, as well as electrical properties at interfaces are examined. The quality of estimates from molecular dynamics and Monte Carlo simulations is validated in comparison to measurements and design rules described where available. The review further describes applications of simulation methods to polymer composite materials, surface modification of nanofillers, and interfacial interactions in building materials. The complexity of functional multiphase materials creates opportunities to further develop accurate force fields, including reactive force fields, and chemically realistic surface models, to enable materials discovery at a million times lower computational cost compared to quantum mechanical methods. The impact of modeling and simulation could further be increased by the advancement of a uniform simulation platform for organic and inorganic compounds across the periodic table and new simulation methods to evaluate system performance in silico.

Catalytic activity of anionic Au–Ag dimer for nitric oxide oxidation: a DFT study

The oxidation of NO is effectively catalyzed by Au–Ag⁻ dimer with Au site is the preferable one.

Slow release of NO by microporous titanosilicate ETS-4

A novel approach to designing nitric oxide (NO) storage and releasing microporous agents based on very stable, zeolite-type silicates possessing framework unsaturated transition-metal centers has been proposed. This idea has been illustrated with ETS-4 [Na(9)Si(12)Ti(5)O(38)(OH)·xH(2)O], a titanosilicate that displays excellent NO adsorption capacity and a slow releasing kinetics. The performance of these materials has been compared to the performance of titanosilicate ETS-10, [(Na,K)(2)Si(5)TiO(13)·xH(2)O], of benchmark zeolites mordenite and CaA, and of natural and pillared clays. DFT periodic calculations have shown that the presence of water in the pores of ETS-4 promotes the NO adsorption at the unsaturated (pentacoordinated) Ti(4+) framework ions.