Journal of Theoretical and Computational Chemistry

The structural stability and mechanical and thermodynamic properties of WII-A₃N₄ (A=C, Si, Ge and Sn) are calculated by first-principles calculations based on the density functional theory. The calculated lattice parameters and elastic constants of WII-A₃N₄ (A=C, Si, Ge and Sn) are in good agreement with the experimental data and previously calculated values. WII-A₃N₄ (A=C, Si, Ge and Sn) compounds are also found to be thermodynamically and mechanically stable. The results suggest that hardness of WII-C₃N₄ is the hardest of these C₃N₄ polymorphs. The hardness of WII-Sn₃N₄ is the smallest among WII-A₃N₄ (A=C, Si, Ge and Sn).

Furthermore, the mechanical anisotropy, Debye temperature, the minimum thermal conductivity and thermodynamic properties of WII-A₃N₄ (A=C, Si, Ge and Sn) compounds can be investigated.

The adsorptions of sulfur trioxide molecule on undoped and N-doped TiO₂ anatase nanoparticles were investigated by density functional theory (DFT) calculations. N-doped nanoparticles were constructed by substitution of oxygen atoms of TiO₂ by nitrogen atoms. The results showed that the adsorption energies of SO₃ on the different nanoparticles following the order N-doped (N site)>N-doped (O_D site)>Undoped (O_D site). We provide the electronic structure of the nanoparticles, as well as complex systems containing the sulfur trioxide molecule and discuss the key issues that influence the adsorption process. The structural properties including the bond lengths, bond angles and adsorption energies and the electronic properties including the projected density of states (PDOSs) and molecular orbitals (MOs) have been mainly analyzed in detail. The obtained results indicate that the interaction between SO₃ molecule and N-doped TiO₂ nanoparticle is stronger than that between SO₃ and undoped nanoparticle, which suggests that N-doping helps to strengthen the interaction of SO₃ with TiO₂ anatase nanoparticles. It is shown that although SO₃ molecule has no significant interaction with undoped nanoparticle, it tends to be strongly adsorbed to N-doped anatase nanoparticles with considerable adsorption energies, being as an effective property to be utilized in gas sensing applications. We also note at this point that the titanium atom and the doped nitrogen atom sites are more active than the dangling oxygen site, which reveals that the titanium and doped nitrogen sites provide more stable adsorption geometries.

In this study, by the density functional theory (DFT) method-based reactivity descriptors, the electronic properties and chemical reactivity of Fe substituted nanocage, FeB_35+nN_36-n(n = 0, 1), were investigated in gaseous and aqueous phases. The calculated binding energies of Fe atoms revealed that the substituting Fe atom in some locations of nanocage make the system more stable. The calculated global descriptors showed that the substituted Fe remarkably increases the chemical reactivity of B₃₆N₃₆. Also, local descriptors showed that the high reactivity of substituted nanocages is mainly related to Fe atom and these chemical species are more talented for nucleophilic attacks. The results of this work may be useful to investigate the effects of substituted metals in chemical reactivity of BN nanostructures.

The triphenylamine (TPA), thiophene and pyrimidine are being used as efficient advanced functional semiconductor materials. In the present study, some new TPA donor–π–acceptor derivatives were designed where TPA moiety acts as donor, thiophene-pyrimidine π-bridge and acetic/cyanoacetic acid as acceptor. The ground-state geometries were optimized at B3LYP/6-31G** level of theory. The excitation energies and oscillator strengths were computed at TD-CAM-B3LYP/6-31G** (polarizable continuum model (PCM), in methanol) level of theory. The electronic, photophysical and charge transport properties were calculated wherever possible the computed values were compared with the available experimental as well as computational data. The electron injection (ΔG^inject), relative electron injection , electron coupling constants (∣V_RP∣) and light harvesting efficiencies (LHE) have been calculated and compared with referenced compounds. The energies of the lowest unoccupied molecular orbitals (E_LUMOs), diagonal bandgaps and energy level offsets were studied to shed light on the electron transport behavior. The effect of anchoring groups (acetic acid and cyanoacetic acid) was studied on the properties of interests in the dye and dye@Ti₆O₁₂. It was observed that after interaction of dye with the TiO₂ cluster intra-molecular charge transport enhanced from HOMO of the dye to LUMO of the semiconductor cluster. The cyanoacetic acid anchoring group leads the superior LHE, ΔG^inject and ∣V_RP∣ which might improve the solar cell performance.

The effect of phonon modes and electron–hole pair (elhp) couplings at different surface temperature on D₂(v = 0, 1; j = 0)–Cu(111) collision has been explored by assuming weakly correlated interactions between molecular Degrees of Freedoms (DOFs) with surface modes and elhp excitations through a Hartree product type wavefunction, where the initial state distributions for the phonon modes and the elhp couplings are incorporated by using Bose–Einstein and Fermi–Dirac probability factors, respectively. We carry out four (4D⊗2D)- and six (6D)- dimensional quantum dynamics on such an effective Hamiltonian, and depict the calculated sticking/transition probabilities and energy transfer from molecule to the surface. The phonon modes slightly affect the sticking probability by broadening the profile, but the transition probability are substantially changed with respect to the rigid surface. On the contrary, the inclusion of elhp coupling along with phonon modes does not change the results much compared to the only phonon case.

A quantum chemical investigation has been performed to spotlight the structure–property relationship among methoxybenzeylidene-based humidity sensor and water molecules. The chemical interactions among (E)-2-(4-(2-(3,4-dimethoxybenzeylidene)hydrazinyl)phenyl) ethane-1,1,2-tricarbonitrile (DMBHPET) sensor and water molecules have been studied using density functional theory (DFT) methods. The molecular structural parameters, binding energies and Infrared (IR) spectroscopic analyses have been performed to assess the nature of intermolecular interactions. Three different positions have been identified for possible attachments of H₂O molecules through hydrogen bonding interactions. These positions include NH (complex 1a), p-OCH₃ (complex 1b) and N=N (complex 1c) group in sensor molecule (1) for the chemical adsorption of water molecules. While, the complex 1abc includes all three sites with simultaneously three H₂O molecules attached to it through hydrogen bonding. The binding energies calculated for complex 1a(NH…H₂O), complex 1b(CH₃O…H₂O), complex 1c(N=N…H₂O) and complex 1abc are -30.97, -18.41, -13.80 and -65.36 kcal/mol, respectively. The counterpoise (CP) scheme has been used to correct the basis set superposition error (BSSE) in calculation of binding energies of sensor and H₂O complexes. The higher binding energy of -65.36 kcal/mol for complex 1abc represents that the present methoxybenzeylidene-based sensor has significant potential through hydrogen bonding formation for sensing humidity as indicated in our previous experimental investigation. The evidence of hydrogen bonding interactions between sensor 1 and H₂O molecules has been traced through structural parameters, red shift in IR spectra as well as molecular electrostatic maps. Thus the present investigation highlights the first computational framework for a molecular level structure-binding activity of a methoxybenzeylidene-based sensor and water molecules.

The absorption wavelengths of the two forms of Rhodamine B, cation and zwitterion, were investigated by Time-Dependent Density Functional Theory (TD-DFT) in combination with polarizable continuum model. The redshift in absorption spectrum of cation relative to zwitterion is attributed to strong inductive effect of carboxyphenyl group and weak electrostatic repulsion between xanthene ring and carboxyphenyl group. The absorption wavelengths of cation and zwitterion decrease linearly with increase of solvent polarity in normal alcohols since in high polar solvents electrostatic repulsion between xanthene ring and carboxyphenyl group increases and affects xanthene π conjugation system. The absorption wavelengths in water and formamide show a deviation from linear relationship because large dielectric constant hinders electrostatic repulsion between carboxyphenyl group and xanthene π system. The hydrogen bonds affect absorption wavelengths because hydrogen bonds could affect conjugation between amino N atoms and xanthene π system or electrostatic repulsion between carboxyphenyl group and xanthene ring. These results indicate electrostatic repulsion between carboxyphenyl group and xanthene ring plays a big role in determining absorption spectrum of Rhodamine B.

The effects of varying halogen and solvent, in terms of vibrational and electronic properties, on the different conformers of 1-pentanamine [CH₃(CH₂)₄NH₂] and 1,1-dihalogeno-pentan-1-amines [CH₃(CH₂)₃CX₂NH₂; X = F, Cl or Br] were investigated by employing the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The B3LYP functional was used with the 6-31++G(d,p) basis set. Computations were focused on the 10 conformational isomers of the compounds in the gas phase and both in non-polar (benzene) and polar (methanol) solvents. The present work explores the effects of the halogen and the medium on the conformational preference, and geometrical parameter, dipole moment, NH₂ vibrational frequency, UV spectrum, highest occupied and lowest unoccupied molecular orbitals (HOMO–LUMO) orbital and DOS diagram of the conformers. The atypical characteristics of fluorine and bromine affecting the electrical bandgap, chemical hardness, electronegativity, PDOS or OPDOS plots and the absorption band are observed correspondingly. The findings of this work can be useful to those systems involving changes in the conformations analogous to the compounds studied.