Chemical Concepts from Density Functional Theory

Chemical concepts such as structure,bonding,reactivity,etc.have been widely used in the literature and text books to appreciate molecular properties and chemical transformations.Even though modern theoretical and computational chemistry is well established from the perspective of accuracy and complexity,how to quantify these concepts is a still unresolved task.Conceptual density functional theory and its related recent developments provide unique opportunities to tackle this problem.In this Special Issue,27 contributions from top investigators over the world are collected to highlight the state-of-art research on this topic,which not only showcases the status of where we are now but also unveils a number to possible future directions to be pursued.

Unraveling the atomic interdiffusion mechanism of NiFe_(2_)O_(4) oxygen carriers during chemical looping CO_(2) conversion

By employing metal oxides as oxygen carriers,chemical looping demonstrates its effectiveness in transferring oxygen between reduction and oxidation environments to partially oxidize fuels into syngas and convert CO_(2) into CO.Generally,NiFe_(2_)O_(4) oxygen carriers have demonstrated remarkable efficiency in chemical looping CO_(2) conversion.Nevertheless,the intricate process of atomic migration and evolution within the internal structure of bimetallic oxygen carriers during continuous high‐temperature redox cycling remains unclear.Consequently,the lack of a fundamental understanding of the complex ionic migration and oxygen transfer associated with energy conversion processes hampers the design of high‐performance oxygen carriers.Thus,in this study,we employed in situ characterization techniques and theoretical calculations to investigate the ion migration behavior and structural evolution in the bulk of NiFe_(2_)O_(4) oxygen carriers during H_(2) reduction and CO_(2)/lab air oxidation cycles.We discovered that during the H_(2) reduction step,lattice oxygen rapidly migrates to vacancy layers to replenish consumed active oxygen species,while Ni leaches from the material and migrates to the surface.During the CO_(2) splitting step,Ni migrates toward the core of the bimetallic oxygen carrier,forming Fe–Ni alloys.During the air oxidation step,Fe–Ni migrates outward,creating a hollow structure owing to the Kirkendall effect triggered by the swift transfer of lattice oxygen.The metal atom migration paths depend on the oxygen transfer rates.These discoveries highlight the significance of regulating the release–recovery rate of lattice oxygen to uphold the structures and reactivity of oxygen carriers.This work offers a comprehensive understanding of the oxidation/reduction‐driven atomic interdiffusion behavior of bimetallic oxygen carriers.

Mo_(2)B_(2)O_(2) MBene for Efficient Electrochemical CO Reduction to C_(2) Chemicals:Computational Exploration

Emerging as a new class of two-dimensional materials with atomically thin layers,MBenes have great potential for many important applications such as energy storage and electrocatalysis.Toward mitigating carbon footprint,there has been increasing interest in CO_(2)/CO conversion on MBenes,but mostly focused on C_(1) products.C^(2+) chemicals generally possess higher energy densities and wider applications than C_(1) counterparts.However,C–C coupling is technically challenging because of high energy requirement and currently few catalysts are suited for this process.Here,we explore electrochemical CO reduction reaction to C_(2) chemicals on Mo_(2)B_(2)O_(2) MBene via density-functional theory calculations.Remarkably,the most favorable CO–COH coupling is revealed to be a spontaneous and barrierless process,making Mo_(2)B_(2)O_(2) an efficient catalyst for C–C coupling.Among C_(1) and C_(2) chemicals,ethanol is predicted to be the primary product.Furthermore,by charge and bond analysis,it is unraveled that there exist significantly more unbonded electrons in the C atom of intermediate*COH than other C_(1) intermediates,which is responsible for the facile C–C coupling.From an atomic scale,this work provides microscopic insight into C–C coupling process and suggests Mo_(2)B_(2)O_(2) a promising catalyst for electrochemical CO reduction to C_(2) chemicals.

Correlation of ^1H NMR Chemical Shift for Aqueous Solutions by Statistical Associating Fluid Theory Association Model

1H NMR chemical shifts of binary aqueous mixtures of acylamide, alcohol, dimethyl sulphoxide (DMSO), and acetone are correlated by statistical associating fluid theory (SAFT) association model. The comparison between SAPT association model and Wilson equation shows that the former is better for dealing with aqueous solutions. Finally, the specialties of both models are discussed.

Analysis of marine ecological compensation for environmental risk caused by chemical spill based on game theory

The problem of marine environmental risk is ultimately the result of game theory between the marine en vironmental managers and the enterprise of potential environmental risk.This paper analyzes the internal economic relationship that whether the"protection"policy is applied between the protection action of marine environmental managers and the chemical enterprise.The result shows that the key factor whether the enterprise adopt the"protec tion"policy or not is the amount of penalty and the government's cost of execution,and the compulsive ecological compensation is obligatory from the angle of stimulating the enterprise of canonical action and adopting the"protec tion"policy.To build the ecological compensation mechanism based on the environmental risk will effectively improve the level of management in sea area and decrease the probability of chemical spill.

Chemical bonding and elastic properties of quaternary arsenide oxides YZnAsO and LaZnAsO investigated by first principles

The structural parameters, chemical bonding and elastic properties of the tetragonal phase quaternary arsenide oxides YZnAsO and LaZnAsO were investigated by using density-functional theory （DFT） within generalized gradient approximation （GGA）. The GGA calculated structural parameters are in agreement with the experimental results. Population analysis suggests that the chemical bonding in YZnAsO and LaZnAsO can be classified as a mixture of ionic and covalent characteristic. Single-crystal elastic constants were calculated and the polycrystalline elastic modules were estimated according to Voigt, Reuss and Hill＇s approximations （VRH）. The result shows that both YZnAsO and LaZnAsO are relatively soft materials exhibiting ductile behavior. The calculated polycrystalline elastic anisotropy result shows that LaZnAsO is more anisotropy in compressibility and YZnAsO is more anisotropy in shear.

Solution-based Chemical Strategies to Purposely Control the Microstructure of Functional Materials

Micro/nanostructured crystals with controlled architectures are desirable for many applications in optics, electronics, biology, medicine, and energy conversions. Low-temperature, aqueous chemical routes have been widely investigated for the synthesis of particles, and arrays of oriented nanorods and nanotubes. In this paper, based on the ideal crystal shapes predicted by the chemical bonding theory, we have developed some potential chemical strategies to tune the microstructure of functional materials, ZnS and Nb205 nanotube arrays, MgO wiskers and nestlike spheres, and cubic phase Cu2O microcrystals were synthesized here to elucidate these strategies. We describe their controlled crystallization processes and illustrate the detailed key factors controlling their growth by examining various reaction parameters. Current results demonstrate that our designed chemical strategies for tuning microstructure of functional materials are applicable to several technologically important materials, and therefore may be used as a versatile and effective route to the controllable synthesis of other inorganic functional materials.

Cattaneo-Christov heat and mass flux model for 3D hydrodynamic flow of chemically reactive Maxwell liquid

This research focuses on the Cattaneo-Christov theory of heat and mass flux for a three-dimensional Maxwell liquid towards a moving surface. An incompressible laminar flow with variable thermal conductivity is considered. The flow generation is due to the bidirectional stretching of sheet. The combined phenomenon of heat and mass transport is accounted. The Cattaneo-Christov model of heat and mass diffusion is used to develop the expressions of energy and mass species. The first-order chemical reaction term in the mass species equation is considered. The boundary layer assumptions lead to the governing mathematical model. The homotopic simulation is adopted to visualize the results of the dimensionless flow equations. The graphs of velocities, temperature, and concentration show the effects of different arising parameters. A numerical benchmark is presented to visualize the convergent values of the computed results. The results show that the concentration and temperature fields are decayed for the Cattaneo^Christov theory of heat and mass diffusion.

Chemical Bond and Nonlinear Optical Effects of Crystals

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Technologies of enhancing oil recovery by chemical flooding in Daqing Oilfield, NE China

By tracking and analyzing the research and practices of chemical flooding carried out in the Daqing Oilfield, NE China since the 1970 s, the chemical flooding theory, technology adaptability and existing problems were systematically summarized, and directions and ideas of development in the future were proposed. In enhanced oil recovery by chemical flooding, the Daqing Oilfield developed theories related to compatibility between crude oil and surfactant that may form ultra-low interfacial tensions with low-acidity oil, and a series of surfactant products were developed independently. The key technologies for chemical flooding such as injection parameter optimization and numerical simulation were established. The technologies of separation injection, cleansing and anti-scaling, preparation and injection, and produced liquid processing were developed. The matching technologies of production engineering and surface facilities were formed. Through implementation of chemical flooding, the Daqing Oilfield achieved outstanding performances with enhanced recovery rate of 12% in polymer flooding and with enhanced recovery rate of 18% in ASP flooding. To further enhance the oil recovery of chemical flooding, three aspects need to be studied:(1) fine characterization of reservoirs;(2) smart and efficient recovery enhancement technologies;(3) environment friendly, high-efficiency and smart matching processes.

A Study of Heavy-Fermion Superconductors via BCS Equations Incorporating Chemical Potential

Heavy-fermion superconductors (HFSCs) are regarded as outside the purview of BCS theory because it is usually constrained by the inequality , where EF, μ, kB, and θD are, respectively, the Fermi energy, chemical potential, Boltzmann constant, and the Debye temperature. We show that this restriction can be removed by incorporating μ into the equations for Tc and the gap Δ0 at T = 0. Further, when μ kBθD, we curtail the limits of the equations for Tc and Δ0 to avoid complex-valued solutions. The resulting equations are applied to a prominent member of the HFSC family, i.e., CeCoIn5, by appealing to ideas due to Born and Karmann, Suhl et al., and Bianconi et al. Since the equations now contain an additional variable μ, we find that 1) the Tc of the SC can be accounted for by a multitude of values of the (μ, λ) pair, λ being the interaction parameter;2) the λ vs. μ plot has a dome-like structure when μ kBθD;3) the (μ, λ) values obtained in 2) lead to reasonable results for the range of each of the following variables: Δ0, s, and n, where s is the ratio of the mass of a conduction electron and the free electron mass and n is the number density of charge carriers in the SC.

A statistical model for predicting thermal chemical reaction rate

A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 （2011）] or molecules [Chin. Phys. Lett. 29 080504 （2012）] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.

Electronic Structures and Chemical Bonding of NbS6^(-/0)Clusters

Density functional theory（DFT） and coupled cluster theory（CCSD（T）） calculations were employed to investigate the structural and electronic properties of Nb S6^- and Nb S6 clusters. Generalized Koopmans＇ theorem was applied to predict the vertical detachment energies and simulate the photoelectron spectra（PES）. The current study indicated that various types of sulfur ligands（i.e., S^（2-）, S^（2-）, S2^（2-） and S3^（2-）） were presented in the lowest-energy structures of Nb S6^（-/0）. The ground-state structure of Nb S6^- is shown to be Cs（~1A＇） symmetry with a terminal S^（2-）, a side-on bound S2^（2-） and a S3^（2-） ligands. Molecular orbital analyses were performed to analyze the chemical bonding in NbS6^（-/0） clusters and elucidate their structural and electronic properties.

Shear Viscosity of Hot QED at Finite Chemical Potential from Kubo Formula

Within the framework of finite temperature field theory this paper discusses the shear viscosity of hot QED plasma through Kubo formula at one-loop skeleton diagram level with a finite chemical potential The effective widths (damping rates) are introduced to regulate the pinch singularities and then gives a reliable estimation of the shear viscous coefficient.The finite chemical potential contributes positively compared to the pure temperature case. The result agrees with that from the kinetics theory qualitatively.

The Algorithm of Chemical Species Analysis for Ab Intio Molecular Dynamics Simulations and Its Application

In ab initio molecular dynamics(AIMD)simulations of chemical reactions,it is important but difficult to identify the chemical species in the trajectory automatically and quickly.In this paper,based on the chemical graph theory,an algorithm for molecular species identification,according to the molecular coordinates and empirical bond length database,is presented.As an example,the chemical species in condensed glycine at room temperature are investigated with our algorithm in detail.The chemical species,including canonical and zwitterionic glycine,their protonated and de-protonated states,and the free protons,are all identified,counted and recorded correctly.Potential applications and further development of the algorithm are also discussed.

Quantum spin Hall insulators in chemically functionalized As(110)and Sb(110)films

We propose a new type of quantum spin Hall （QSH） insulator in chemically functionalized As （110） and Sb （110） film. According to first-principles calculations, we find that metallic As （110） and Sb （110） films become QSH insulators after being chemically functionalized by hydrogen （H） or halogen （C1 and Br） atoms. The energy gaps of the functionalized films range from 0.121 eV to 0.304 eV, which are sufficiently large for practical applications at room temperature. The energy gaps originate from the spin-orbit coupling （SOC）. The energy gap increases linearly with the increase of the SOC strength λ/λ0. The Z2 invariant and the penetration depth of the edge states are also calculated and studied for the functionalized films.

A theoretical study on chemical ordering of 38-atom trimetallic Pd-Ag-Pt nanoalloys

In this study,truncated octahedron(TO)structure is selected for further analysis and we focus on 38-atom Pd-Pt-Ag trimetallic nanoalloys.The best chemical ordering structures of PdnAg32-nPt6 trimetallic nanoalloys are obtained at Gupta level.The structures with the lowest energy at Gupta level are then re-optimized by density functional theory(DFT)relaxations and DFT results confirm the Gupta level calculations with small shifts on bond lengths indicating TO structure is favorable for 38-atom of PdnAg32-nPt6 trimetallic nanoalloys.The DFT excess energy analysis shows that Pd8Ag24Pt6 composition has the lowest excess energy value in common with excess energy analysis at Gupta level.In Pd8Ag24Pt6 composition,eight Pd atoms are central sites of 8(111)hexagonal facets of TO,24 Ag atoms locate on surface,and 6 Pt atoms locate at the core of the structure.It is also obtained that all of the compositions except Pd18Ag14Pt6 and Pd20Ag12Pt6 exhibit a octahedral Pt core.Besides,it is observed that there is a clear tendency for Ag atoms to segregate to the surface and also Pt atoms prefer to locate at core due to order parameter(R)variations.

Comparative Study of the Chemical Reactivity of Helical Peptide Models for Protein Glycation

Non-enzymatic glycation of proteins has been implicated as an important cause of the complications associated with diabetes and Alzheimer disease. It is well known that glycation involves the reactivity of, primarily, the ε-amino group of the lysines present in the protein. The immediate chemical environment of an amino group modulates the glycation reaction. In this work, several model helical peptides for protein glycation has been studied by resorting to QM:MM calculations through the ONIOM methodology. Some Conceptual DFT descriptors have been calculated that allowed the comparison of the chemical reactivity between the different model peptides in terms of the position of the Lys group and other spatially proximate amino acid residues.

CCSD(T) study on the structures and chemical bonds of AnO molecules (An = Bk–Lr)

The molecular geometries and dissociation energies of AnO (An = Bk–Lr) molecules were first obtained at thecoupled-cluster single-, double-, and perturbative triple-excitations [CCSD(T)] level of theory. Four hybrid functionals,B3LYP, M06-2X, TPSSh, and PBE0, were also employed in the calculations for the sake of comparison. In comparison ofthe CCSD(T) results, B3LYP, TPSSh, and PBE0 functionals can obtain more appropriate results than M06-2X and MP2.The analyses on molecular orbitals show that the 7s, 6d, and 5f atomic orbitals of actinide (An) atoms participate in thebonding of An–O bonds. The partial covalent nature between An and O atoms is revealed by QTAIM analyses.

Ab Initio Prediction of ^(29)Si-NMR Chemical Shifts

The ability of several ab initio models to predict experimental 29Si-NMR chemical shift is examined. The shielding values of trimethylsilyl chloride (A), t-butyldimethylsilyl chloride (B) and allyltrimethylsilane (C) are calculated by GIAO , CSGT and IGAIM methods, using HF/6-31G*, B3LYP/6-31G*, HF/6-311+G **, B3LYP/6-311+G ** and MPW1PW91/6-311+G ** models respectively. The 29Si chemical shifts calculated by GIAO method using HF/6-311+G ** model are highly in agreement with those obtained experimentally. All of the models above reproduce the trends of chemical shifts in all cases studied, suggesting that the models are of practical value.