Hybrid Density Functional Method Research Articles

Predicting decomposition temperatures and carbonization feasibility of heterocycles with their decomposition mechanism

Pyrolysis of heterocyclic compounds such as Meldrum’s acid derivatives was studied with two key mechanisms analysing their energy barrier diagrams by the hybrid density functional theory method M06-2X. The feasibility of these decomposition reactions was calculated specifically for Meldrum’s acid, monomethyl Meldrum’s acid, dimethyl Meldrum’s acid (DMMA), methylene Meldrum’s acid (MeMA) and (dimethylamino)methylene Meldrum’s acid (DMAMeMA), based on previous experimental analysis. Their initial decomposition products (ketene or substituted ketenes with CO2 and acetone) were found endothermic requiring activation energies (∼180–––230 kJ/mol) at the decomposition temperatures of 280, 299, 301, 503 and 414 K respectively. The transition state theory calculations show MeMA and DMAMeMA are thermally more stable than other derivatives with low values for the rate constants and high energy barriers to produce initial decomposition products, suggesting they can produce fine carbon materials during carbonization. DMMA is found the best option for obtaining heteroatoms-doped carbon material formation.

Predicting decomposition temperatures and carbonization feasibility of heterocycles with their decomposition mechanism

Pyrolysis of heterocyclic compounds such as Meldrum’s acid derivatives was studied with two key mechanisms analysing their energy barrier diagrams by the hybrid density functional theory method M06-2X. The feasibility of these decomposition reactions was calculated specifically for Meldrum’s acid, monomethyl Meldrum’s acid, dimethyl Meldrum’s acid (DMMA), methylene Meldrum’s acid (MeMA) and (dimethylamino)methylene Meldrum’s acid (DMAMeMA), based on previous experimental analysis. Their initial decomposition products (ketene or substituted ketenes with CO2 and acetone) were found endothermic requiring activation energies (∼180–––230 kJ/mol) at the decomposition temperatures of 280, 299, 301, 503 and 414 K respectively. The transition state theory calculations show MeMA and DMAMeMA are thermally more stable than other derivatives with low values for the rate constants and high energy barriers to produce initial decomposition products, suggesting they can produce fine carbon materials during carbonization. DMMA is found the best option for obtaining heteroatoms-doped carbon material formation.

Essential oils from fennel plants as valuable chemical products: gas chromatography–mass spectrometry, FTIR, quantum mechanical investigation, and antifungal activity

AbstractIn the present study, the biomass produced by fennel plants (Foeniculum vulgare Mill.) was converted to yield bioactive chemicals, and the hydrodistillation method was used to extract the essential oils (EOs) from both the leaves and the umbels. The antifungal activity of the EOs was tested using bioassay against the development of Fusarium oxysporum MW854649 and Alternaria solani MT279570. Molecular spectroscopic detection techniques were used to evaluate the EO products using gas chromatography–mass spectrometer (GC–MS) and Fourier transform infrared spectroscopy (FTIR). GC–MS equipped with single quadruple analyzers have been used to measure the electron ionization (EI) mass spectra of the primary constituents of fennel EOs at 70 eV. The main chemical compounds in the EO from leaves were anethole, estragole, D-limonene, trans-β-ocimene, and fenchone, with percentages of 37.94, 35.56, 17.46, 1.53, and 1.49%, respectively. The abundant compounds in the EO from umbels were estragole, anethole, D-limonene, fenchone, and γ-terpinene, with percentages of 51.18, 25.08, 12.22, 6.57, and 2.86%, respectively. EI mass spectral fragmentation of the major compounds D-limonene, estragole, anethole, and fenchone has been investigated. Umbels and leaf EOs at 5000 mg/L displayed the strongest suppression of fungal growth against A. solani, with values of 87.78% and 79.63%, respectively, compared to the positive control (94.44%). The EOs from umbels and leaves at 5000 mg/L showed the highest inhibition of fungal growth against F. oxysprium as compared to the positive control (94.44%), with values of 77.77% and 72.96%, respectively. All of the important ions—including a few distinctive fragment ions—have comprehensive fragmentation pathways defined. Based on EI, the main routes of fragmentation for the primary compounds have been identified. The existence of alkenes, aliphatic alcohols, ethers, carboxylic acids, ester compounds, alkanes, hydrogen-bonded alcohols, and phenols was demonstrated by the FTIR analysis of fennel EOs. On the other hand, the reactive behavior of the studied molecules has been investigated using two quantum mechanics method: the modified neglect of diatomic overlap (MNDO), a semi-empirical method, and the density functional theory (DFT)/B3LYP hybrid density functional method with the 6-311G (d, p) basis set in the ground state for gas phase. The optimum geometries have been obtained through the execution of computations and electrostatic potential. The obtained analytical and calculated results were then used to understand the activity of the studied EOs in further medical applications.

Hybrid Density Functional Valence Bond Method with Multistate Treatment.

Recently, a hybrid density functional valence bond (VB) method, λ-DFVB(U), has been proposed and shown to give accuracy that is comparable to that of CASPT2 in calculations of atomization energies, atomic excitation energies, and reaction barriers, while its computational cost is approximately the same as the valence bond self-consistent-field (VBSCF) method. However, the interaction between electronic states is not included in λ-DFVB(U) since the last step of λ-DFVB(U) is not a diagonalization of the Hamiltonian matrix on the electronic state basis. Therefore, λ-DFVB(U) gives the wrong topology of the potential energy surfaces (PESs) near the conical intersection region. In the present paper, we propose a novel hybrid density functional VB method with multistate treatment, named λ-DFVB(MS), in which an effective Hamiltonian matrix is constructed on the basis of the diabatic states obtained by the valence-bond-based compression approach for the diabatization scheme, and the interaction between electronic states can be included through the diagonalization of the effective Hamiltonian matrix. Test calculations show that λ-DFVB(MS) gives the correct topology of the PESs near the conical intersection region. We also show that the VBSCF wave function with selected VB structures can be applied as a reference in λ-DFVB(MS).

Accurate prediction of semiconductor bandgaps based on machine learning and prediction of bandgaps for two-dimensional heterojunctions

The bandgap value of materials has a profound impact on their properties and applications. Presently, with the development of high-throughput calculations, the bandgap of most materials is simulated and calculated using the density functional theory (DFT). Nevertheless, the bandgap of materials calculated in this way is often accompanied by large errors and long time consuming. Besides, the bandgap results obtained in different experimental environments are different. Therefore, finding a method to calculate the material bandgaps quickly and accurately is imminent. In this work, the Machine Learning (ML) method is used to predict the bandgap of semiconductor materials. Four different machine learning models are trained and tested through the feature processing, which can accurately predict the bandgap of the material by the hybrid density functional (HSE06) method, of which the average mean absolute error (MAE) is 0.142 eV and the coefficient of determination (R2) is 0.977. Moreover, in order to better predict the bandgap of local small-sample semiconductor materials, the federal learning framework is employed to forecast small-sample datasets under different experimental conditions. Then, the four ML models are used to the prediction of materials and compared the results with the local calculation results. The results indicate that the bandgap error of compound semiconductor materials is 2∼10%, and the bandgap error of 2D heterojunctions semiconductor materials is 5∼30%. In addition, the ML models are also utilized to the Materials Project database, in which the bandgap of about 53170 semiconductor materials is successfully predicted. In conclusion, the work not only provides a method to accurately predict the bandgap of compound semiconductor materials, but also supplies an effective idea for the prediction of the bandgap of semiconductor materials in local small data sets, which accelerating the development of the application of semiconductor materials.

Elastic Properties of Binary d-Metal Oxides Studied by Hybrid Density Functional Methods

Elastic Properties of Binary d-Metal Oxides Studied by Hybrid Density Functional Methods

Investigation on the photocatalytic property of direct Z-type van der Waals g-C3N4/AlN heterojunction and its mechanism

Using hybrid density functional method, the electronic, interfacial and optical characters of the g-C3N4/AlN heterojunction as well as the effect of electric field and biaxial strain on its photocatalytic performance were systematically studied. The g-C3N4/AlN is a direct band gap semiconductor (2.71 eV) with stagger band alignment structure and exhibits direct Z-scheme photocatalytic reaction mechanism. Under the external electric field and biaxial strain, the staggered band feature of the heterostructure is retained and its VBM potential and CBM potential still have strong oxidation and reduction capabilities, which can meet the redox potential conditions of photocatalytic water-splitting. Meanwhile, the band gap gradually decreases with the increase of electric field strength ranged from −0.5 V/Å to 0.5 V/Å and 1% compressible strain tunes the heterostructure from direct band gap to indirect band gap. Our work provides a theoretical basis for the design of g-C3N4-based heterojunctions with high photocatalytic performance.

Study on the optical and electrical properties of Fe-doped CuAlO2 with first-principles

Fe-doped is an effective method to improve the conductivity of p-type transparent conductive oxide (TCO). In this paper, we performed first-principle calculations to study the effect of Fe-doped on the electrical structure and optical properties of the CuAlO2 crystal. To get accurate results, we used the finite size correction scheme (FNV method) to correct the defect formation energy for charged defects and the hybrid density functional method was used to adjust the band edge. The calculation results show that the formation energy for Fe occupying Al position (marked as FeAl) in CuAlO2 is lower than that for Fe occupying Cu position (marked as FeCu) and FeAl is the easiest one to form. It is also found that Fe-doping can increase the hole concentration of CuAlO2 and thus increasing the conductivity of the CuAlO2 crystal. Furthermore, we have investigated the optical spectrum of Fe-doped CuAlO2 and the absorption peak of CuAlO2 with FeAl∙∙ locates at 2.07 eV, which is close to the experimental data (2.10 eV). It can be inferred that the transmittance of the material decreases and the light absorption increases in the visible range.

Theoretical insights into the defect performance of the wide bandgap semiconductor BaS.

Wide bandgap semiconductors materials (WBGSMs) are of great interest for their applications in transparent electronics and power electronics. Recent studies have shown that BaS is a potential transparent conducting material but the knowledge of it is deficient. Herein, we systemically investigate its electronic structure and evaluate the effects of its intrinsic defects and extrinsic dopants by utilizing the hybrid density functional method. The obtained results show that BaS is an indirect bandgap semiconductor with a bandgap of 3.88 eV. Its electron-effective mass is very small (0.33 m0). We find that the intrinsic n-type conductivity of BaS is connected with the shallow donor defect sulfur vacancy (VS). Regarding extrinsic dopants (group IA atoms), we find that Li and Na are favorable n-type dopants, while K and Rb are p-type dopants. Among these impurities, the Li interstitial (Liint) configuration possesses the lowest formation energy of 0.114 eV. Based on thermodynamic simulations, we find that the electron density can reach 2.39 × 1020 cm-3 in Li-doped BaS at room temperature, which is comparable to those of typical WBGSMs In2O3, BaSnO3, and β-Ga2O3. We expect BaS could replace typical WBGSMs in some applications. Moreover, its component elements Ba and S are non-toxic, cheap, and earth-abundant, making it a very competitive candidate for WBGSMs. Based on these results, we deem BaS a promising candidate for optoelectronic applications.

Insights into the photocatalytic mechanism of S-scheme g-C3N4/BiOBr heterojunction

The energy band alignment and photocatalytic performance of g-C3N4/(0 0 1)-BiOBr heterojunction are studied based on the first-principles HSE06 hybrid density functional method. Our results show that g-C3N4 and BiOBr are staggered near the forbidden band of the heterojunction. The built-in electric field (BEF) is formed with the direction from the g-C3N4 surface to the BiOBr surface. Under visible light irradiation, the existence of BEF makes the photogenerated electrons in the conduction band minimum (CBM) of BiOBr migrate across the interface region of g-C3N4/(0 0 1)-BiOBr heterojunction to reach the valence band maximum (VBM) of g-C3N4 to achieve the effective separation of photogenerated electron-hole pairs. g-C3N4/(0 0 1)-BiOBr heterojunction is an S(step)-scheme photocatalytic mechanism and a large number of photogenerated electrons come from the BiOBr will greatly improve the hydrogen production activity in the g-C3N4 surface, which is consistent with the previous experimental observations. Moreover, we predict that g-C3N4/(0 0 1)-BiOBr heterojunction has better hydrogen production efficiency and photocatalytic performance than g-C3N4/(0 0 1)-BiOCl heterojunction. Our work can provide an effective scheme and theoretical supports for the design of novel S-scheme heterojunction photocatalysts.

λ-DFVB(U): A hybrid density functional valence bond method based on unpaired electron density.

In this paper, a hybrid density functional valence bond method based on unpaired electron density, called λ-DFVB(U), is presented, which is a combination of the valence bond self-consistent field (VBSCF) method and Kohn-Sham density functional theory. In λ-DFVB(U), the double-counting error of electron correlation is mitigated by a linear decomposition of the electron-electron interaction using a parameter λ, which is a function of an index based on the number of effectively unpaired electrons. In addition, λ-DFVB(U) is based on the approximation that correlation functionals in KS-DFT only cover dynamic correlation and exchange functionals mimic some amount of static correlation. Furthermore, effective spin densities constructed from unpaired density are used to address the symmetry dilemma problem in λ-DFVB(U). The method is applied to test calculations of atomization energies, atomic excitation energies, and reaction barriers. It is shown that the accuracy of λ-DFVB(U) is comparable to that of CASPT2, while its computational cost is approximately the same as VBSCF.

Exploring and modeling the ion mobility spectrometry of perindopril: Example of protonation-dissociation reactions in large molecules.

The current research is constructed for considering the chemical ionization and dissociation of perindopril in the positive mode of corona discharge ion mobility spectrometry. Four product ion peaks are observed in the ion mobility spectrum of perindopril erbumine at the cell temperature of 473 K. These peaks are assigned through the obtained intensity variation analysis in the ion mobility spectra over the elapsed time accompanied by the calculations backed by the validated density functional theory (DFT). In this regard, the most stable ionic species associated with each peak and the corresponding reliable generation pathways are found by the well-confirmed meta hybrid density functional method, M06-2X. The peaks are assigned to the protonated perindopril and its dissociation products, including counter ion and the related fragment ions. However, the structures of the neutral perindopril in the gas phase are thoroughly assessed to find a more stable one. The predicted chemical ionization products by the theory are in excellent agreement with our presented experiment here. Theoretical evaluations demonstrated that the production of a fragment by dissociation process occurs when perindopril gets a proton from the ionization region. Also, without protons, there is no dissociation process. Therefore, our mechanism investigated here is the proton transfer one. All possible sites of perindopril are considered theoretically for protonation along with their possible reactions. In addition to the computed PES, the assigned ions for obtained spectra are confirmed by the computed equilibrium constants and rate constants. Our theoretical results show that the peak of the main fragment is for M-CH3 CH2 OH produced by a reaction pathway involving no barrier. This study opens new perspectives in interpreting large molecules spectra for future studies.

Structural Properties and Magnetic Ground States of 100 Binary d-Metal Oxides Studied by Hybrid Density Functional Methods.

d-metal oxides play a crucial role in numerous technological applications and show a great variety of magnetic properties. We have systematically investigated the structural properties, magnetic ground states, and fundamental electronic properties of 100 binary d-metal oxides using hybrid density functional methods and localized basis sets composed of Gaussian-type functions. The calculated properties are compared with experimental information in all cases where experimental data are available. The used PBE0 hybrid density functional method describes the structural properties of the studied d-metal oxides well, except in the case of molecular oxides with weak intermolecular forces between the molecular units. Empirical D3 dispersion correction does not improve the structural description of the molecular oxides. We provide a database of optimized geometries and magnetic ground states to facilitate future studies on the more complex properties of the binary d-metal oxides.

Effect of the Dopant Configuration on the Electronic Transport Properties of Nitrogen-Doped Carbon Nanotubes.

Nitrogen-doped carbon nanotubes (N-CNTs) show promise in several applications related to catalysis and electrochemistry. In particular, N-CNTs with a single nitrogen dopant in the unit cell have been extensively studied computationally, but the structure-property correlations between the relative positions of several nitrogen dopants and the electronic transport properties of N-CNTs have not been systematically investigated with accurate hybrid density functional methods. We use hybrid density functional theory and semiclassical Boltzmann transport theory to systematically investigate the effect of different substitutional nitrogen doping configurations on the electrical conductivity of N-CNTs. Our results indicate significant variation in the electrical conductivity and the relative energies of the different dopant configurations. The findings can be utilized in the optimization of electrical transport properties of N-CNTs.

Data-driven modeling of S0 → S1 excitation energy in the BODIPY chemical space: High-throughput computation, quantum machine learning, and inverse design.

Derivatives of BODIPY are popular fluorophores due to their synthetic feasibility, structural rigidity, high quantum yield, and tunable spectroscopic properties. While the characteristic absorption maximum of BODIPY is at 2.5eV, combinations of functional groups and substitution sites can shift the peak position by ±1eV. Time-dependent long-range corrected hybrid density functional methods can model the lowest excitation energies offering a semi-quantitative precision of ±0.3eV. Alas, the chemical space of BODIPYs stemming from combinatorial introduction of-even a few dozen-substituents is too large for brute-force high-throughput modeling. To navigate this vast space, we select 77 412 molecules and train a kernel-based quantum machine learning model providing <2% hold-out error. Further reuse of the results presented here to navigate the entire BODIPY universe comprising over 253 giga (253 × 109) molecules is demonstrated by inverse-designing candidates with desired target excitation energies.

Novel Carboxylic Acid Functionalized Dendronized Polymer: A Homogeneous, Reusable Metal Free Acid Catalyst for the Synthesis of Symmetric and Unsymmetric Xanthene Derivatives

AbstractIn the present study, carboxylic acid‐functionalized tris(hydroxymethyl)propane initiated polyepichlorohydrin cored dendronized polymer (TMP‐PECH‐COOH) was successfully synthesized. Successful incorporation of carboxylic acid functionality was evidenced by Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TG/DTG), and NMR spectroscopy (1H NMR). Thermodynamic properties such as thermal energy, enthalpy, and Gibb's free energy as well as global reactivity descriptors such as chemical potential, chemical hardness, and electrophilicity index of the TMP‐PECH‐COOH dendronized polymer were investigated using Gaussian 09 program employing the hybrid density functional B3LYP method and 6‐31G basis set. The synthesized dendronized polymer (TMP‐PECH‐COOH) could act as a metal‐free acid catalyst for catalyzing the reactions for the synthesis of 1,8‐dioxooctahydroxanthenes and tetrahydrobenzoxanthene‐11‐ones under mild reaction conditions in an aqueous medium. The catalyst could be reused at least six times making the present procedure facile, practical, and sustainable. In addition, the efficiency of the present catalyst was compared with some previous reports.

Determining the Band Alignment at the BiVO4|NiOOH Interface Using the Hybrid DFT Technique

It is important to understand the band offsets between semiconductors, which are crucial to determine the direction of electron transfer at the interfaces. Two methods are normally used to determine the direction from the first principles: alternating slabs put in contact (without empty spaces between them) and separate calculations for each material surface in the presence of vacuum spaces. The first method may introduce distortions due to insufficient epitaxial match, which may lead to bandgap changes, and the second may neglect electron transfer at the interface, which may be important in systems exhibiting very different average electronegativities. This can also imply a spill of electronic density into the vacuum spaces, which will not be present at real interfaces. Herein, both approaches were used to study the BiVO4/NiOOH interface, and the results were compared; the results are here relevant for photoelectrochemistry. The method is based on hybrid Density Functional Theory methods which give for the bulk phases Bandgap values that agree with the experimental ones (in one case, a value reflecting the theoretical value). The distances between the (hybrid DFT-derived) band positions and the corresponding profiles of the Hartree electrostatic potential were transferred to the interfaces. This helps determining the appropriate positions of the valence and conduction bands (as has been suggested by C. G. Van de Walle &amp; R. M. Martin, Phys. Rev. B 1987, 35, 8154). It is ensured that the interfaces are nonpolar (Tasker’s criterion: P.W. Tasker, J. Phys. C: Solid State Phys. 1979, 12, 4977).

A computer-aided method for controlling chemical resistance of drugs using RRKM theory in the liquid phase

The chemical resistance of drugs against any change in their composition and studying the rate of multiwell-multichannel reactions in the liquid phase, respectively, are the important challenges of pharmacology and chemistry. In this article, we investigate two challenges together through studying drug stability against its unimolecular reactions in the liquid phase. Accordingly, multiwell-multichannel reactions based on 1,4-H shifts are designed for simplified drugs such as 3-hydroxyl-1H-pyrrol-2(5H)-one, 3-hydroxyfuran-2(5H)-one, and 3-hydroxythiophen-2(5H)-one. After that, the reverse and forward rate constants are calculated by using the Rice Ramsperger Kassel Marcus theory (RRKM) and Eckart tunneling correction over the 298–360 K temperature range. Eventually, using the obtained rate constants, we can judge drug resistance versus structural changes. To attain the goals, the potential energy surfaces of all reactions are computed by the complete basis set-quadratic Becke3 composite method, CBS-QB3, and the high-performance meta hybrid density functional method, M06-2X, along with the universal Solvation Model based on solute electron Density, SMD, due to providing more precise and efficient results for the barrier heights and thermodynamic studies. To find the main reaction pathway of the intramolecular 1,4-H shifts in the target molecules, all possible reaction pathways are considered mechanistically in the liquid phase. Also, the direct dynamics calculations that carry out by RRKM theory on the modeled pathways are used to distinguish the main reaction pathway. As the main finding of this research, the results of quantum chemical calculations accompanied by the RRKM/Eckart rate constants are used to predict the stability of drugs. This study proposes a new way to examine drug stability by the computer-aided reaction design of target drugs. Our results show that 3-hydroxyfuran-2(5H)-one based drugs are the most stable and 3-hydroxythiophen-2(5H)-one based drugs are more stable than 3-hydroxy-1H-pyrrol-2 (5H)-one based drugs in water solution.

Electromechanical Characteristics by a Vertical Flip of C70 Fullerene Prolate Spheroid in a Single-Electron Transistor: Hybrid Density Functional Methods.

In this study, the B3LYP hybrid density functional theory was used to investigate the electromechanical characteristics of C70 fullerene with and without point charges to model the effect of the surface of the gate electrode in a C70 single-electron transistor (SET). To understand electron tunneling through C70 fullerene species in a single-C70 transistor, descriptors of geometrical atomic structures and frontier molecular orbitals were analyzed. The findings regarding the node planes of the lowest unoccupied molecular orbitals (LUMOs) of C70 and both the highest occupied molecular orbitals (HOMOs) and the LUMO of the C70 anion suggest that electron tunneling of pristine C70 prolate spheroidal fullerene could be better in the major axis orientation when facing the gate electrode than in the major (longer) axis orientation when facing the Au source and drain electrodes. In addition, we explored the effect on the geometrical atomic structure of C70 by a single-electron addition, in which the maximum change for the distance between two carbon sites of C70 is 0.02 Å.

A database of electron-impact ionization cross sections of molecules composed of H, C, N, O, and F

Electron-impact ionization cross sections are essential parameters required in various plasma models. To provide self-consistent ionization cross sections in plasma modeling, an open database with tabular fitting parameters and an online web system are established in this work. There are 88 species composed of H, C, N, O, and F in this database. The Binary-Encounter-Bethe (BEB) model, the Deutsch-Märk (DM) model, and the combined model which consolidates the BEB and DM models are considered to obtain the atomic and molecular ionization cross sections. The input parameters of the above models for all the species are calculated according to the quantum chemical computation with the hybrid density functional theory method with the Austin–Petersson–Frisch functional including dispersion. The same methods and basis set ensure consistent ionization cross sections in the database. The average relative error between the calculated and experimental ionization potential is 1.84%. The average root-mean-square error of the fitted ionization cross sections is 1.81% with respect to the exact values predicted by the combined model. The online database can be accessed from the website http://plasma.mathboylinlin.com/db/cs/ion/.