Bulk SiC phases with tetrahedral arrangements have been identified several decades ago, and have been widely studied due to their potential applications. Until recently, Yaghoubi et al.’s experimental results (Chem. Mater. 2018, 30, 7234) showed that the graphitic SiC with few SiC layers stacking is stable. In this work, we further explore the potential application of graphitic SiC as the Na-ion battery anode via the first-principle simulation. Our results reveal that the theoretical capacity of graphitic SiC reaches up to 1339.44 mAh/g, which is almost the highest among the already known Na-ion battery anodes. Together with the low diffusion barrier, moderate open circuit voltage and excellent electronic conductivity during the sodiation, we propose that the graphitic SiC is a promising material as Na-ion battery anode. More importantly, we find that the intercalation strength of Na ions into C-based multi-layer materials (or the corresponding theoretical capacity, the operation voltage) could be enhanced by increasing the amount of covalent components in Na‒C bonds, which could be realized via doping by atom (such as Li, Be, B, Al, Si or P) with lower electronegativity than that of C atom.
Photovoltaic properties of the natural dyes of chlorophylls consist of Chl a, Chl b, Chl c2, Chl d, Phe a, Phe y and Mg-Phe a, were studied in the gas phases and water. The extension of the π-conjugated system, the substitution of the central Mg2+ and proper functional groups in the chlorophyll structures can amplify the charge transfer and photovoltaic performance. Chl a shows more favorable dynamics of charge transfer than other studied chlorophylls. Chl d, Phe a, Phe y and Mg-Phe a, have a greater rate of the exciton dissociation in comparison with Chl a, Chl b, and Chl c2 originated from a lower electronic chemical hardness, a lower exciton binding energy, and a bigger electron-hole radius. As a result, better efficiencies of the light-harvesting and energy conversion of the chlorophylls mainly appear in the Soret band. The LHE values of the chlorophylls in water show that solvent favorably affects the ability of light-harvesting of the photosensitizers. Finally, based on the energy conversion efficiency, Chl a, Phe a, and Mg-Phe a, are proposed as the best candidates for using in the dye-sensitized solar cells.
A systematic benchmark of phosphorus and fluorine NMR chemical shifts predictions at six different density functional theory (DFT) / the gauge-including atomic orbital (GIAO) methods was conducted. Two databases were compiled: one consists of 35 phosphorus-containing molecules, which cover the most common intra-molecular bonding environments of trivalent and pentavalent phosphorus atoms; the other is composed of 46 fluorine-containing molecules. The characteristics of each DFT/GIAO method with different solvent models were demonstrated in details. The application of linear regression between the calculated isotropic shielding constants and experimental chemical shifts was applicable to improve the prediction accuracy. And, the best methods with the SMD and CPCM implicit solvent models for 31P chemical shifts predictions, are able to yield a root-mean-square deviation (RMSDs) of 5.58 ppm and 5.42 ppm, respectively; for 19F, the corresponding lowest prediction errors with these two applied solvent models are 4.43 ppm and 4.12 ppm. The developed scaling factors fitted from linear regression are applicable to enhance the chance of successful structural elucidations of phosphorus or fluorine-containing compounds, as an efficient complement to 13C, 1H, 11B and 15N chemical shifts predictions.
Density functional theory (DFT) calculations were conducted to investigate mechanistic details of ethanol-to-butadiene conversion reaction over MgO or ZnO catalyst. We evaluated the Lewis acidity and basicity of MgO and ZnO and found that ZnO had the stronger Lewis acidity and basicity compared with those of MgO. Potential energy surfaces (PESs) of ethanol-to-butadiene conversion, which included relevant transition states (TSs) and intermediates, were computed in detail following the generally accepted mechanism reported in the literature, where such mechanism included ethanol dehydrogenation, aldol condensation, Meerwein-Pondorf-Verley (MPV) reduction and crotyl alcohol dehydration. DFT results showed that ethanol dehydrogenation was the rate limiting step of overall reaction when the reaction was catalyzed by MgO. Also, DFT results showed that ethanol dehydrogenation occurred more easily on ZnO compared with MgO where such a result correlated with the stronger Lewis acidity of ZnO. In addition, we computed ethanol dehydration which generates ethylene, one of the major undesired side reaction products for butadiene formation. DFT results showed that ZnO favored dehydrogenation over dehydration while MgO favored dehydration.
In our work, the formation energies, band structures, densities of states, effective masses and optical absorption properties of pure BiOBr and 3d transition metals-doped BiOBr have been calculated using DFT+U method. Ti, V, Fe, Cr, Co, Ni and Cu doping can induce impurity energy levels, originating from spin-up or -down orbits of 3d TMs, within the forbidden band of BiOBr, but Sc, Mn and Zn atoms only change the electronic delocalization in the valence bandor conduction band region of BiOBr. Furthermore, with introduction of 3d TMs atoms, there exist the redshift phenomena for optical absorption band edge of BiOBr to different extents. The photo response priority order, structural stability and recombination probability of photoinduced carriers for 3d TMs-doped BiOBr are summarized. Our theoretical findings should well explain the experimental observations in the previous literatures, and provide promising prediction and significant guidance for the well-construction of BiOBr-based photocatalyst systems.
This work presents analytical and numerical results for the position- and momentum-space information entropies, of the 1s2-state of helium-like ions, using different interaction potentials. The potentials that we used are the Yukawa potential (YP), and the exponential-cosine-screened Coulomb potential (ECSCP). The investigated studies allow us to relate the position-space information with the momentum-space information of Shannon and Fisher, as well as Shannon entropy power, and the Fisher-Shannon information product, through different famous relations. The calculation is done using the one-electron charge density of entangled two-parameter wave function. On one hand, the results that are presented for ten members in the helium isoelectronic sequence demonstrate with precision the effect of correlation on bare charge distributions. On the other hand, it leads to some very important results for both the correlated and uncorrelated values of the informatic entropies. Analytical formula for the momentum-space information entropies are given. The effect of the nuclear charge and the screening parameter on the information expressions has been studied for both potentials. Detailed computational and numerical values and characteristics of these information quantities, as a function of the screening parameter, are reported here for the ﬁrst time. New inequality has been proposed with Fisher’s total value to measure the correlation of two electrons.
The emission of carbon dioxide in large amounts is commonly believed to be the main cause of global climate changes. Development of CO2 capture processes is still a big current challenge. Some anions have been studied for the gas sequestration process due their great affinity to CO2. In this work, electronic structure calculations were performed at the MP2/aug-cc-pvtz level to compute the interaction between 20 anions and CO2. A CBS scheme, using extrapolated energies, was also employed for both gas phase and solvent calculations. The reactions between the anions and CO2 were therefore studied in four different conditions (gas phase, toluene, tetrahydrofuran and water). The trends observed for the reaction thermodynamics with the MP2 method is similar to that observed previously with the B3LYP-D3 and M06-2X functionals. The reactions in the gas phase are highly exothermic and do not involve any activation energy. The solvent effect reduces the exothermicity and induces an intrinsic activation barrier. The negative charge is dispersed in the adduct, leading to a weaker interaction in a polar solvent. Then, increasing the medium polarity, the energy difference between the adduct and the reactants decreases. We also observed a limit for solvent stabilization in the low dielectric constant range. For example, the results obtained with tetrahydrofuran are closer to those obtained with water than to those obtained with toluene. Considering both the thermodynamics of the reaction and the differential solvent effects, we were able to indicate anions derived from alkyl sulfides as the most convenient for CO2 sequestration among the set here considered.
A systemic investigation of the substitution and cooperative effects on the P…N π-hole pnicogen bond were performed via theoretical calculations. The structural and energetic properties of the binary complexes between a series of substituted benzonitrile and PO2F have been examined to study the substitution effect. The stability of the binary complexes increases in the order of CN
Due to it is potential application in the field of high energy density materials, how to stabilize cyclopentazolate anion (cyclo-N5-) has attracted many interests theoretically and experimentally. Therefore, a series of ion salts containing [cyclo-N5]- were synthesized and studied. The instability of [cyclo-N5]- is caused by the five lone pairs of electrons localized on five neighbored N atoms. In this work, we expect if the [cyclo-N5]- can be stabilized by the coordination with acidic ligands, by weakening the multi repulsion from the lone pairs to stabilize the [cyclo-N5]-. The two compounds of [N5(BH3)5]-, and [N5(AgCN)5]- have been designed and compared based on the Lewis acid-base theory. [N5(H2O)5]- is designed to evaluate the effect of hydrogen bond in the stabilization. For all the structures, we study the bonding properties and thermal stabilities based on the analysis of electronic structures and Car-Parrinello molecular dynamics (CPMD) simulations. The results indicate it is a effective method to stabilize [cyclo-N5]- by introducing the Lewis acid. Our insights on [cyclo-N5]- compounds with high thermal stability under ambient conditions will provide a new idea for the research and synthesis of new high energetic [cyclo-N5]- series compounds.
Transition metal porphyrazines are a widely used class of compounds with applications in catalysis, organic solar cells, photodynamic therapy and nonlinear optics. The most prominent members of that family of compounds are metallophtalocyanines that have been subject of numerous spectroscopic and theoretical studies. In this work, the electronic structure and X-ray absorption characteristics of three Cu-porphyrazine derivatives are investigated by means of modern electronic structure theory. More precisely, the experimentally observed N K-edge and Cu L-edge features are presented and reproduced by time-dependent density functional theory, restricted open-shell configuration interaction and a restricted active space approach. Where possible, the calculations are used to interpret the observed spectroscopic features in terms of electronic transitions and furthermore connect spectral differences to chemical variations. Part of the discussion of the computational results concerns the impact of various parameters and approximations that enter the calculations, e.g. the choice of active space.
Investigation of cooperative effect exhibited by purely C-H—O hydrogen bonded (H-bonded) networks in linear and cyclic clusters of (1,3-cyclohexanedione)n (n = 2 to 6) has been carried out using density functional theoretical calculations. Linear clusters were found to show anti-cooperative behavior, while the cyclic clusters showed positive cooperativity. H-bond strengths and binding energies per bimolecular interaction were found to decrease with increasing cluster size for the linear clusters whereas their cyclic counterparts showed opposite trends. The extent of cooperativity has been found to show monotonic behavior for both linear and cyclic clusters and was found to reach an asymptotic limit with increasing cluster size. Natural bond orbital (NBO) analysis and atoms in molecule (AIM) calculations were found to corroborate the obtained results.
Li‐rich layered Mn‐based oxide (LMO) cathode materials, with the formation of Li2MnO3, have attracted much attention due to their potential in various applications with high energy density. However, these cathode materials for Lithium‐ion batteries still suffer from drawbacks such as poor rate capability and voltage decay, which makes further investigation vital and rational. Here, the doping strategy is employed to investigate the effect of TM = Ti, Cu, and Zn on Li2Mn0.5TM0.5O3 cathode materials for improving electrochemical performances of Li2MnO3. Electrochemical properties such as voltage, electrical conductivity, safety, structural stability, and kinetics and mechanism of Li‐ion diffusion are evaluated and compared. All doped cathodes decrease the voltage reduction and improve the electrical conductivity coefficient in comparison with LMO. Doping Cu notably increases the electrical conductivity of LMO by 77%. Ti doping exhibits the potential to increase the maximum voltage of LMO and structural stability. Doping Zn and Cu elements can delay the oxygen loss significantly, which leads to a higher life cycle and safety. In addition, doping Zn is expected to have a higher Li‐ion diffusion coefficient due to its low energy barrier and partial charge of oxygen atoms in its cathode structure. This first‐principle study of doping effects of TM = Ti, Cu, and Zn with α = 0.5 in Li2Mn0.5TMαO3 may be a useful leading study for further investigation into the synthesis of lithium‐rich materials with enhanced electrochemical performance.
The ligand-promoted palladium-catalyzed hydroarylation of alkynes with arenes without directing group is able to furnish alkenyl chlorides via a 1,4-chlorine migration or trisubstituted alkenes. This reaction is challenging due to bidentate N, N ligand and electron-neutral arenes have rarely been reported to afford good yields. We carried out density functional theory calculations to better understand the elementary steps of the reaction and unveil the ligand effects and origin of substituent-controlled chemoselectivity of challenging C-H activation. For the n-propyl-substituted substrate, CMD process is the rate-determining step of the catalytic reaction. And the chemoselectivity is controlled by oxidative addition with the C-Cl bond cleavage and protonation process. However, for the reaction with 3,5-dimethylphenyl-substituented substrate, the key step of the whole catalytic cycle is the protonation process. The stronger electrostatic attractions, repulsive force and aryl substituent effects result in reverse chemoselectivity. Bidentate ligand L1 (2-OH-1,10-phenanthroline) reacts with Pd(OAc)2 to form a most stable square-planer species, which is different from the one formed by ligand L2(1,10-phenanthroline). The steric repulsion are found to be mainly responsible for no product with L2 as the ligand, which is different from as proviously reported.
Ab initio calculations on systems involving singlet molecular oxygen (O2 (1g)) are challenging due to signicant multi-reference character arising from the degeneracy of the HOMO and LUMO orbitals in singlet oxygen. Here we investigate the stragegy of bypassing singlet oxygen’s multi-reference character by simply adding the experimen- tally determined singlet/triplet splitting (22.5 kcal/mol) to the triplet ground state of molecular oxygen. This method is tested by calculating rate constants for the reac- tions of singlet molecular oxygen with furan, 2-methylfuran, 2,5-dimethylfuran, pyrrole, 2-methylpyrrole, 2,5-dimethylpyrrole, and cyclopentadiene. The calculated rate con- stants are within a factor of 15 compared to experimentally determined rate constants. The results show that energy renement at the CCSD(T)-F12 level of theory is cru- cial to achieving accurate results. The reasonable agreement with experimental values validates the bypassing approach which can be used for other systems involving the 1,4-cyclo-addition of singlet oxygen. 2
Hydrogen peroxide (H2O2), as clean oxidant, has long suffered from low efficiency and selectivity for the oxidation of olefins. In the present paper, the redox important ferrate anion (FeO42-) has been anchored into a silanol-decorated polyoxometalates (POM) to form single–site supported Fe-POM catalyst. And possible reaction mechanism for the epoxidation of propylene with hydrogen peroxide (H2O2) catalyzed by the Fe-POM catalyst have been investigated based on density functional theory with M06L functional. The study of molecular geometry, electronic structure, and bonding feature shows that the Fe-POM complex can be viewed as a high-valent Fe-oxo (Fe=O) species. The propylene molecule was activated by the Fe-POM catalyst via an effective electron transfer from propylene to the Fe-POM catalyst to form a cation propylene radical. Due to the high reactivity of radical species, the calculated activation energy barrier is only 4.50 kcal mol-1 for epoxidation of propylene to epoxypropane catalyzed by the Fe-POM catalyst. Subsequently, the calculated free energy profiles show that H2O2 was decomposed into a H2O molecule and a surface O species over the Fe-POM catalyst, and the remaining O atom attaches to the exposed the Fe center, resulting in the replenishing of Fe-POM catalyst via a two-state reaction pathway. The calculated activation energy barrier for this process is 23.42 kcal mol–1, and thus decomposition of H2O2 is the rate-determining step for the whole reaction. The Fe center serves as an electron acceptor, accepting electrons from the binding propylene molecule to form radical species in the first half of the reaction, and acts as the role of electron donor in the rest reaction steps to eliminate the radical feature, reduce the reactivity, and stop the reaction at the stage of the desired epoxypropane product.
The mechanisms of rhodium-catalyzed coupling reaction of ketoxime and 1,3-enynes were investigated by employing the density functional theory (DFT) calculations. Different 1,3-enynes would lead to different annulation products. Reaction A undergoes five sequential steps (C-H activation, 1,3-enyne migratory insertion, 1,4-Rh migration, cyclization, and deprotonation) to lead to [4 + 1] annulation product. Whereas, due to the electronic effect, the process generating [4 + 2] product in reaction A is restricted. In contrast, the electron-withdrawing group of N(Me)2 group in 1,3-enyne would bring about the [4 + 2] annulation product in reaction B. Our calculated results indicate that no [4 + 1] annulation product could be obtained in reaction C, in agreement with the experimental observation that the cis-allyl hydrogen in 1,3-enyne is crucial for the [4 + 1] annulation reaction.
Based on the combination of novel carbon material graphynes (GYs) and superalkalis (OM3), a class of graphyne superalkali complexes, OM3+@(GY/GDY/GTY)– (M = Li, Na, and K), have been designed and investigated by density functional theory method. Computational results reveal that these complexes with high stability can be regarded as novel superalkali salts of graphynes due to electron transfer from OM3 to GYs. For second order nonlinear optical response, these superalkali salts exhibit large first hyperpolarizabilities (β0). Two important effects on β0 values are found, namely the atomic number of alkali atom in superalkali and the pore size of graphyne. Integrating the two effects, the selected combination of OLi3 with large pore size GTY can bring the considerable β0 value (6.5×105 au), which is a new record for superatom-doped graphynes. In the resulting complex, the OLi3 molecule is located at the center of the pore of GTY, forming a planar structure with the highest stability among these salts. Besides large β0 values, these superalkali salts of graphynes have deep-ultraviolet working region, hence can be considered as a new kind of high-performance deep-ultraviolet NLO molecules.
We systematically investigate the binding nature of CB towards 20 amino acids in both neutral (AAs) and protonated (AAs+) states by quantum chemistry methods. The result indicates molecular recognition process are enthalpy-driven. Among AAs, Arg and Asn shows the largest binding strength to CB, and for AAs+, Gln+ and Asn+ bind to CB the strongest. The binding strength of protonated CB/AA+ is much stronger than that of neutral CB/AA counterpart, due to the introduction of ion-dipole interaction and the increase number and strength of hydrogen bonds. Energy decomposition analysis (EDA) indicates that electrostatic interactions play major roles in both CB/AAs and CB/AAs+ complexes. Moreover, we analyzed the dependence of binding strength on single AA volume and dipole moment. This study is benefit for providing valuable information in predicting the recognition sites for sequence-based peptide or protein by CB and rationally designing synthetic host molecule for specific peptide or protein recognition.