Journal of Theoretical and Computational Chemistry

Geometrical and molecular electronic structure calculations on a series of metal free organic dyes based on triphenylamine (TPA) moiety have been performed using the TD-DFT methods. The B3LYP/6-31G, B3LYP/6-31G(d,p), M06-HF/6-31G(d,p) and WB97XD/6-31G(d,p) levels of theory have been utilized to predict the relationships between chemical structure and theoretically calculated molecular electronic properties of the studied dyes which may help in optimizing the properties of TPA-based photosensitizers in DSSCs. The solvation process of these dyes has been taken into account by means of the polarizable continuum model. The light harvesting efficiency, the free energy change for the electron injection process to the surface of TiO₂ nanocrystalline semiconductor and the open circuit potential are calculated using all of these methods in different media. Significant charge transfer character of the HOMO → LUMO electronic transition which dominates the S_o → S₁ vertical excitation in these systems facilitates the electron transfer process to the surface of TiO₂. The results of the present computations are reported and discussed.

The hydrogen sulfide adsorption and dissociation on pure Pd (111) and Au (111), alloy Pd/Au (111) and Au/Pd (111) surfaces have been investigated using the pseudo-potential plane wave method within the generalized-gradient approximation density functional theory (GGA+DFT). The results show that H₂S tends to be adsorbed on top site, HS prefers to locate on bridge site, and the S and H locate on fcc site on various surfaces. Compared the adsorption of sulfur-containing species and hydrogen on pure and alloy metal surfaces, a similar trend of adsorption energies on the metal surfaces (Pd/Au (111) >Pd (111) >Au (111) >Au/Pd (111)) is found. In addition, the dissociation process on the Pd (111) and Pd/Au (111) surfaces is predicted to be exothermic. However, on Au (111) and Au/Pd (111), the dissociation process is endothermic. The work reveals that H₂S dissociation is more likely to happen on Pd/Au (111) surface. Finally, the adsorption energies of adsorbate on metal surfaces have strong correlation with the d-band center. The d-band center moves away from the Fermi level, and the adsorption energy decreases. According to the LDOS analysis, the inner Au atoms of Pd/Au (111) can enhance the top-layer d-band intensity, whereas the inner Pd atoms of Au/Pd (111) cause the opposite effect. The further electronic state analysis reveals the interaction between H₂S and metal surfaces.

We studied the interfacial features of 1-butene/water and extraction process of 2-butanol by molecular dynamics (MD) simulations. The infinite dilute diffusion coefficients of 1-butene in water is larger than that of 2-butanol, and one important reason is that 2-butanol molecules can form hydrogen bonds with water molecules. 1-butene is more soluble in water under supercritical condition than that under subcritical condition. 1-butene under supercritical condition can extract more 2-butanol from aqueous solution than that under other conditions. A process of producing 2-butanol by the direct hydration of 1-butene is more competive when it operates under the supercritical conditions of 1-butene which due to a higher solubility of 1-butene in water, a larger diffusion coefficient of 1-butene and a lower 2-butanol concentration in water.

The genetic algorithm based on the Multi-Niche Crowding (MNC) method is used with the semi-empirical methods AM1 and PM3 in order to scan the potential energy surface (PES) of neutral and protonated glycine. The algorithm is implemented as a package of programs interfaced with MOPAC and piloted by scripts. Both methods AM1 and PM3 located six minima on the PES of neutral glycine and seven on the protonated glycine one, of which three are those of the N-protonated form and four of the O-protonated one.

The pnicogen bonding interactions of PCl₃ and π-electron systems (acetylene, ethylene, benzene) were calculated by using MP2/aug-cc-pVDZ method and the effect of hydrogen bond on pnicogen bond systems were investigated. It has been indicated that the hydrogen bonding and the pnicogen bonding interactions have influence on each other and the positively cooperative effect has been detected. The interaction energies of pnicogen bonded supramolecular system were also calculated by using DFT method (M06-2X) and some simple comparisons with those by using MP2 method were made. It has been disclosed from natural bond orbitals (NBO) analysis that more the amount of charge transfer of pnicogen bonding interaction, the greater the stability of the corresponding complex. Through AIM topological analysis, it has been revealed that the electron density of pnicogen bond BCP point is positively correlated with the stability of trimeric complex. Electron localization function (ELF) was also adopted to analyze the nature of pnicogen bonding interactions. Furthermore, density difference function (DDF) method was adopted to analyze the variation of electron density of pnicogen bond system because of hydrogen bond.

First-principles calculations based on the density functional theory (DFT) within the generalized gradient approximation have been used in the present research. Fluorine doping in the SnO₂ crystals has been carried out considering a number of different defect concentrations. Dopant influence upon structural, electronic and electrical properties of the tin dioxide has been discussed in detail. The system presents n-type electrical conductivity relating our work directly to a number of empirical studies in this area. An experimental fact that n-type conductivity tends to decrease at rather high fluorine impurity rates has been explained at the theoretical level.

The In-doped GaN is investigated by first-principles calculations of plane wave ultra-soft pseudo-potential method based on the density functional theory (DFT). The band structure, electronic structure, density of states and optical properties are investigated. The results indicate that the band-gap becomes narrower and the absorption edge of optical properties is red-shifted with the increase in In-doped concentration. Meanwhile, the visible region has strong absorption properties, and the significant absorption peaks are observed near 3.0 eV and 6.1 eV. The other peaks correspond to the wavelength of absorption spectra from the ultraviolet portion extending to the infrared portion, which almost covers the entire solar spectrum. The studied results show that In-doped GaN can be applied as solar cell and transparent conductivity material.

DFT studies have been carried out for the cycloaddition reactions of a cyclic nitrone, 1-pyrroline-1-oxide and an acyclic nitrone, C,N-diphenyl nitrone to an unsymmetrically disubstituted dipolarophile, 1-cinnamoyl-1-piperidine. These reactions proved to be opposite to each other with respect to the electron demand character predicted by the electronic chemical potentials, electrophilicities and charge transfer at the transition states. The regio- and stereoselectivities have been predicted from DFT based reactivity indices, interaction energy calculations using a perturbative orbital independent theoretical model and the activation parameters of the located transition states. Two different concepts have been used for the evaluation of interaction energies. The selectivities were found to be in conformity with the experimental findings. The time gaps between the formations of C–C and C–O bonds were evaluated from single trajectory simulations. The asynchronicity of bond formation process was analyzed from the wiberg bond indices, atom–atom overlap weighted NAO bond orders and the calculated asymmetry indices of the transition states.