Journal of Theoretical and Computational Chemistry

The layered structural model was proposed to study the geometry and electronic properties of the (WO₃)_x/(TiO₂)_y heterostructures in this paper. The geometry and electronic properties were affected greatly by the relative proportion of TiO₂ and WO₃ in the nanocomposites. The minimum band gap of (WO₃)_x/(TiO₂)_y heterostructures decreased with the proportion of WO₃ increasing but increased with the proportion of TiO₂ increasing. Interestingly, electrons at the upper valence band (VB) can be directly excited from 2p and 3d orbitals of titania to the conduction band (CB), which was mainly consisted of 5d orbitals of tungsten trioxide. The effective electron mass of (WO₃)_x/(TiO₂)_y heterostructures was higher than that of pure TiO₂. It indicated that the electron–hole recombination rate of hybrid (WO₃)_x/(TiO₂)_y heterostructure was lower than that of pure TiO₂, which might imply that photocatalytic activities of the hybrid (WO₃)_x/(TiO₂)_y heterostructures were enhanced under visible light irradiation. The theoretical results might offer a new useful guide for designing semiconductors photocatalyst, such as heterostructure nanocomposites.

Diarylamines (Ar₂NH) are generally used as antioxidants to inhibit or retard the auto-oxidation degradation of lubricating oil by trapping ROO• radicals. In the present study, 20 kinds of 4,4′-disubstituted diphenylamine compounds were investigated through density functional theory (DFT) calculations. The results indicate that the N–H bond dissociation enthalpy (BDE) linearly correlates its one-electron oxidation potential, the difference in Mulliken atomic charge on the two atoms of N–H bond, the reaction rate constant of hydrogen transfer from Ar₂NH to peroxy radical, and the chemical hardness of the resulted Ar₂N• radical, respectively. The substitution of alkyl groups (electron-donating groups) decreases the N–H BDE, one-electron oxidation potential and the reaction rate constant, while that of significant electron-withdrawing groups such as -NO₂ and -COOCH₃ increases these three parameters. The electron-donating groups such as alkyls could improve the antioxidation performance of 4,4′-disubstitued diphenylamines whereas electron-withdrawing groups have the contrary effect. In addition, the frontier molecular orbital of Ar₂NH has been also analyzed.

Geometries associated with relative stabilities and energy gaps of the Mo-doped boron clusters have been investigated systematically by using density functional theory. The critical size of Mo-encapsulated B_n structures emerges as n = 10, the evaluated relative stabilities in term of the calculated fragmentation energies reveal that the MoB₆ has enhanced stabilities over their neighboring clusters. Furthermore, the calculated polarities of the MoB_n reveal that the hypercoordinated planar MoB₁₀ wheel is a weakened polar molecule and MoB₁₁ ring is a nonpolar molecule, and aromatic properties are discussed. Additionally, the MoB₁₀ cluster with smaller highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap is supposed to be stronger chemical activity and smaller chemical hardness. Moreover, the recorded natural populations show that the charges transfer from boron framework to Mo atom. It should be pointed out that the remarkable charge-transfer features of MoB_n clusters are distinctly similar to those of transitional metal (TM)-doped Si_n clusters; growth-pattern of the TMB_n depends on the doped TM impurity.

The structure characteristics, interaction energies, cooperative energies of the complexes between chalcogen hydrides (H₂Y) and halogen hydrides (HX) have been studied theoretically at the MP2 level with aug-cc-pVTZ basis set in this paper. The conclusions show that there are strong interactions between H₂Y and HX. The stability of the complex is decided by the electronegativity of the negatively charged atom. The cooperativity is observed in the two or three hydrogen bonds of each trimer structures in title system. The values of the cooperative energies and the cooperative contributions all illustrate that the cooperativity is of great importance in these complexes. The "atoms in molecules" (AIM) analyses show that the complexes in title system are mainly electrostatic interactions (closed-shell interactions) in character. For H⋯O bonds in H₂O⋯HF⋯H₂O, H₂O⋯HBr⋯H₂O and HF⋯H₂O⋯HF, the 1 < |V_c|/G_c < 2 and -G_c < H_c < 0 indicate the interactions in these compounds are between closed-shell interaction and opened-shell interaction.

The geometries, electronic structures and energies of small TiSi_n species (n = 1–8) and their anions were systematically investigated by G4 theory. The ground-state structures of these clusters are presented herein. For neutral TiSi_n (n = 1–8), the spin multiplicities of the ground-state structures are singlet, with the exception of n = 2, which exists in a triplet state. For anionic TiSi_n^-, the spin multiplicities of the ground-state structures are doublet, with the exception of n = 2, which is quartet. The adiabatic electron affinities for TiSi_n are estimated to be 1.31 eV (TiSi), 1.46 eV (TiSi₂), 1.53 eV (TiSi₃), 1.71 eV (TiSi₄), 2.06 eV (TiSi₅), 2.16 eV (TiSi₆), 2.20 eV (TiSi₇) and 2.39 eV (TiSi₈). In comparison with the available experimental data, the calculated adiabatic electron affinities differ from experimental values by an average absolute deviation of only 0.03 eV. Additionally, the dissociation energies of Ti atoms from TiSi_n, and Si atoms from TiSi_n and Si_n clusters are estimated to examine relative stabilities.

A number of Λ shaped complexes of alkaline earth metals Be, Mg and Ca with varying terminal groups have been considered for the theoretical study of their second hyperpolarizability. The chosen complexes are found to be sufficiently stable and for a chosen ligand the stability decreases in the order: Be-complex > Ca-complex > Mg-complex. The calculated results of second hyperpolarizability obtained at different DFT functionals for the 6-311++G(d,p) basis set are found to be fairly consistent. The Λ shaped ligands upon complex formation with metals lead to strong enhancement of second hyperpolarizability. The highest magnitude of cubic polarizability has been predicted for the metal complex having > C(C₂H₅)₂ group. For a chosen ligand, the magnitude of second hyperpolarizability increases in the order Be-complex < Mg-complex < Ca-complex which is the order of increasing size and electropositive character of the metal. The variation of second hyperpolarizability among the investigated metal complexes has been explained in terms of the transition energy and transition moment associated with the most intense electronic transition.

Many Poisson–Boltzmann equation (PBE) solvers have been developed to calculate electrostatic energy of biomolecules, and each PBE solver has its advantages. In this study two PBE solvers — DelPhi and PBSA module in AMBER — are compared in terms of calculation results, convergence and program-running time by calculating the electrostatic solvation energy for a test set composed of 4 Kirkwood models and another test set of 25 protein structures. The protein structures were pretreated by AMBER and AMBER99SB force field parameters were used in all calculations. It is found that (i) At fine grids, both PBE solvers can produce accurate results on test set 1 and consistent results with each other on test set 2, with differences between each other varying from several to ~ 10 kcal/mol. (ii) Under convergence criterion "absolute value of relative error is less than or equal to 2% (|RE| ≤ 2%)", both PBE solvers need very fine grids to produce convergent results on small and complex Kirkwood models, while grid spacings of ≤ 0.5 Å–0.6 Å are well enough for them to achieve good convergent results on various molecular structures. We recommend users to adopt such grid spacing in using of these PBE solvers so as to get good enough convergent results. (iii) In terms of time consumption, DelPhi appears to be more time-saving than PBSA. In summary, according to our comparison, DelPhi and PBSA are paralleled good PBE solvers. The convergence of PBSA is a little better than DelPhi, while DelPhi exceeds PBSA in running speed.

In this work, the tautomeric transformations and reactivity of isoindole and sila-isoindole molecules has been explored using the B3LYP/6-311G(d,p) level of theory in gas and solution phases. These calculations show that isoindole isomer has more stability rather than 1-h-isoindole. There is identical trend in silated species. The frontier molecular orbitals (FMO) and band gap energy calculations were performed at the B3LYP/6-311G(d,p) level in gas and various solvent. Solvent effects have been analyzed by using the self-consistent reaction field (SCRF) method based on polarizable continuum model (PCM) in chloroform, chlorobenzene, dichloromethane and tetrahydrofurane. Thermodynamic parameters calculated at room temperature have been analyzed. Also, electron affinities were computed. Local reactivity descriptors as Fukui functions local softness and electrophilicity indices analyses are performed to find out the reactive sites within molecule. Density functional theory (DFT) calculations were performed to compute nitrogen-14 nuclear quadrupole resonance (NQR) spectroscopy parameters.

Molecular Incorporation is an important approach of providing novel compounds with fascinating structures. In this paper, we theoretically described the incorporation of the central planar tetracoordinate molecules NAl₄^- or CAl₄^2- into borane cluster B₁₀H₁₄. By molecular orbital analysis, a novel four-fold Al–H bonding interaction was found, and it contributes to the molecular incorporation. In addition, we found that the counterion Li⁺ is critical for the neutral incorporation species, due to its small atomic radii and little positive charge. To measure the nonlinear optical (NLO) response, the static first hyperpolarizabilities (β₀) were evaluated at the second-order Møller–Plesset (MP2) level. The β₀ values are 1708 a.u and 8682 a.u for [B₁₀H₁₄⋯NAl₄]^- and [B₁₀H₁₄⋯CAl₄]^2-, respectively, which indicates that the charge plays a significant role on deciding the value of β₀. Moreover, it is different for the change of β₀ value brought by counterion Li⁺. Li⁺ decreases the β₀ value of [B₁₀H₁₄⋯CAl₄]^2-, while it increases the β₀ value of [B₁₀H₁₄⋯NAl₄]^-, therein, the sandwich-like B₁₀H₁₄–Li–NAl₄(I) exhibits considerable β₀ value (31,253 a.u.). This reveals that it is possible to explore high-performance NLO materials based on suitable molecular incorporation. Besides, the present study is also expected to enrich the knowledge of the planar tetracoordinate carbon chemistry and boron chemistry.

The equilibrium geometric structures, relative stabilities and electronic properties of negatively charged lead telluride clusters are systematically investigated using density functional theory (DFT). The result offered both vertical and adiabatic detachment energies (VDEs and ADEs) for these clusters, divulging an outline of alternating values in which odd n clusters exhibited higher values than even n clusters. Simulations found the negatively charged lead telluride clusters with even n to be thermodynamically more stable than their immediate odd n neighbors, with a consistent pattern also being found in their HOMO–LUMO (HL) gaps. Analysis of the clusters dissociation energies found at cluster to be the preferred product of the queried fragmentation processes, consistent with our finding that cluster exhibits enhanced stability. Beyond n = 12, this study showed that the negatively charged (PbTe)_n clusters in the size range n = 13 – 20, prefer two-dimensional stacking of face-sharing lead telluride cubical units, where lead and tellurium atoms possess a maximum of five-fold coordination. The preference for six-fold coordination, which is observed in the bulk, was not observed at these cluster sizes.

Two new salts 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate and 1-methyl-3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate were designed based on the structures of experimentally synthesized 3-azido-1,2,4-triazolium 5-nitro-tetrazolate and 1-methyl-3-azido-1,2,4-triazolium 5-nitro-tetrazolate, to explore new promising candidates for energetic materials and to investigate the influences of the substituents (-CH₃ and -N₃) and solvent (water) on the intramolecular interactions and properties. The intramolecular hydrogen bonding interactions were investigated by the natural bond orbital (NBO) and the quantum theory of atoms in molecules (QTAIM) analyses using the density functional theory (DFT) and the dispersion correction DFT (DFT-D) methods. The low-lying singlet electronic transitions were estimated using the time-dependent DFT. All four examined salts exist as ionic structures in aqueous solution while acid–base molecular complexes form in gas phase. The hydrogen bond energy (E_H) obtained with the DFT-D method is larger than that obtained with the DFT method, but the trend is consistent, i.e. -N₃ increases while -CH₃ decreases E_H. In addition, the position of the strongest electronic absorption peak has a little correlation with the number of -N₃ and -CH₃ groups. 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate is a valuable energetic salt with the highest nitrogen content, oxygen coefficient and density and the second highest heat of formation and chemical stability.

Reaction mechanisms were proposed in this study for the theoretical synthesis of high-energy 1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin (TNAD). Corresponding computations were performed using density functional theory (DFT) and the Hartree Fock (HF) method with the same 6-31G(d,p) base function. Glyoxal and ethylenediamine were used as the raw materials and were placed into respective gaseous and solvated (water or ethanol) environments to proceed the condensation reaction to form the precursor 1,4,5,8-tetraazadecalin, which subsequently underwent four stages of nitro-group substitution to obtain the target TNAD compound. A whole reaction scheme closely related to the experimental processes was successfully constructed, and the corresponding energy barriers were estimated for each elementary reaction. The findings revealed that the overall activation energy by B3LYP/6-31G(d,p) calculation is 2660.4 kJ/mol, which is lower than the 2832.1 kJ/mol calculated by HF/6-31G(d,p) computation. Furthermore, the reaction has a lower overall energy barrier in the solvated environment than in the gaseous system, being 2389.6 kJ/mol in ethanol, 2428.7 kJ/mol in water and 2660.4 kJ/mol in the gaseous phase. The ethanol-solvated system is suggested to be the most suitable medium for the synthesis of TNAD.