Quantum Simulations of Preferable H2O Dissociation Pathway on the Ru-Alloyed Pt(111) Surface Based on Density Functional Theory

Reaction pathways for a water molecule dissociation (H2Oads) to form hydroxyl (OHads) and hydrogen (Hads) on the Ru-alloyed Pt(111) surface were computationally modelled on the basis of density functional theory (DFT). The aim of this study was to evaluate whether or not such a reaction can take place and to determine the most probable route for this reaction. To get the answer, we calculated the potential energy surfaces (PES) of the proposed reaction pathways. From the results of the PES scan, we then obtained the most preferential pathway for H2O dissociation, i.e., the reaction route with an activation energy of 0.72 eV. This activation energy value is lower than the value of pure Pt (111), the surface at which H2O dissociation can occur in the real system. Thus, it can be said that water splitting may be easier when catalyzing Ru-alloyed surfaces compared to pure Pt catalysts.

Crystal structure, spectral characterization, molecular modeling studies and structural effects of the proton transfer process for (E)-5-methoxy-2-[(3,4-dimethylphenylimino) methyl]phenol

The main purpose of this study is to characterize a new organic material, (E)-5-methoxy-2-[(3,4-dimethylphenylimino)methyl]phenol, which was synthesized and grown as a single crystal. The molecular structure and spectroscopic properties of the ortho-hydroxy Schiff base compound were determined by X-ray diffraction analysis, Fourier-transform infrared (FT-IR), ultraviolet-visible (UV-Vis) and nuclear magnetic resonance (NMR) spectroscopy techniques, experimentally and computationally with density functional theory (DFT) calculations. X-ray and UV-Vis studies show that the compound exists in an OH tautomeric form in the solid and solvent media. The gas phase geometry optimizations of two possible forms of the title compound, resulting from the prototropic tautomerism, were obtained using DFT calculations at the B3LYP/6-311G+(d,p) level of theory. A relaxed potential energy surface (PES) scan was performed based on the optimized geometry of the OH tautomeric form by varying the redundant internal coordinate, the O-H bond distance. According to the PES scan process, the molecular geometry is strongly affected by the intramolecular proton transfer. The calculated first hyperpolarizability indicates that the compound could be a good material for non-linear optical applications.

Ab initio prediction of the polymorphic structures of pyrazinamide: A validation study

A validation study to predict the possible stable polymorphs of Pyrazinamide within a low energy conformational region of the flexible torsion angle was made through a potential energy surface (PES) scan by gas phase optimisation using the MP2/6-31G(d,p) method. Hypothetical crystal structures with favourable packing density for each of the stable conformers generated from the PES scan were generated using a global search with a repulsion only potential field. The densest crystal structures with stable energy were analyzed with more accurate lattice energy minimisation via distributed multipole analysis using a repulsion-dispersion potential. The stability of the predicted crystal structures with similar close packing to the known experimental polymorphs of Pyrazinamide molecule was analyzed by inspecting their intermolecular short contacts. Studies to analyze the second derivative mechanical properties from the hessian matrix were carried out to emphasise the thermodynamic stability of predicted polymorphs of Pyrazinamide.

Experimental (FT-IR and FT-Raman) and spectroscopic investigations, electronic properties and conformational analysis by PES scan on 2-methoxy-5-nitrophenol and 2-methoxy-4-methylphenol

A complete vibrational and molecular structure analysis is performed based on the quantum mechanical approach by HF and DFT calculations.

Potential Energy Surface (PES) Scan of Gas-Phase L-Proline

We performed here a systematic ab initio calculations on neutral gas-phase L-proline. A total of 8 local minima were located by geometry optimization of the trial structures using density functional theory (DFT) with B3LYP three parameter hybrid potential coupled with the 6-31G)d( basis set. The absolute minimum obtained will be subject to a rigid potential energy surface (PES) scan by rotating its carboxylic group using the same method with more accurate basis set B3LYP/6-311++G(d,p), to get a deeper idea about its conformational stability. The main aim of the present work was the study of the rigidity of the L-proline structure and the puckering of its pyrrolidine ring.