Renan Augusto Pontes Ribeiro

Synthesis, antimicrobial activity and advances in structure-activity relationships (SARs) of novel tri-substituted thiazole derivatives.

Trisubstituted thiazoles were synthesized and studied for their antimicrobial activity and supported by theoretical calculations. In addition, MIC, MBC and MFC were also tested. Moreover, the present study was analyzed to scrutinize comprehensive structure-activity relationships. In fact, LUMO orbital energy and orbital orientation was reliable to explain their antibacterial and antifungal assay. Amongst the tested compounds, tri-methyl-substituted thiazole compound showed higher antimicrobial activity and low MIC value due to highest LUMO energy.

Photoelectrochemical and theoretical investigation of the photocatalytic activity of TiO2 : N

Electrochemical and photoelectrochemical techniques have been employed to investigate the electronic energy level modification of N-doped TiO2 and to elucidate its properties and roles, particularly the electron transfer rate and influence on recombination, in a simple and facile manner. However, the results obtained cannot be easily interpreted and they need comparisons with theoretical calculations. In this study, photoelectrochemical measurements were conducted to investigate the effect of N-doping on TiO2 nanomaterials, and the results obtained were compared with theoretical calculations. Band-gap values calculated by diffuse reflectance UV-vis spectroscopy were used together with photoelectrochemical measurements of TiO2 and TiO2 : N flat-band potentials to create a scheme of the energy-level band edges. In addition, this method confirmed the creation of energetic inter-levels by the N-doping process, as predicted by theoretical calculations. The replacement of an oxygen atom by nitrogen atom in the anatase structure shows a modification of the energetic levels, caused by a shift of the upper energy level; this shift was caused by local structural disorder. From the photoelectrochemical results, it is possible to confirm that the electron concentration in the TiO2 photoelectrode is higher than that in the TiO2 : N photoelectrode; due to an increase in the recombination of electrons and holes because of the creation of inter-levels in the TiO2 : N band-gap. In addition, theoretical analysis indicated a possibility of direct transfer of electrons into the band-gap of TiO2 : N. This combined approach was useful for interpreting many unclear results with respect to the photocatalytic activity of TiO2 : N.

Structural, electronic and elastic properties of FeBO3 (B = Ti, Sn, Si, Zr) ilmenite: a density functional theory study

FeBO3 (B = Ti, Sn, Si, Zr) materials were simulated from Density Functional Theory (DFT) with the B3LYP hybrid functional to investigate the B-site replacement effect on the ilmenite structure. Lattice parameters, bond distances, bulk-modulus, density of states (DOS), Mulliken population analysis and charge density maps were examined. Calculated structural parameters were in agreement with experimental results and revealed that the unit cell volume was controlled by the ionic radius of the B-site metals. The bulk-modulus obtained indicated that these results were influenced by different material densities. The electronic results showed that the band-gap and structural stability were influenced by the energy levels and electronegativity of the metals occupying the B-site, as shown in the literature. Mulliken population analysis and charge density maps show the magnetic property for a Fe atom in the d6 configuration and charge corridor formation in the [001] direction due to the intermetallic connection.

The role of exchange–correlation functional on the description of multiferroic properties using density functional theory: the ATiO3 (A = Mn, Fe, Ni) case study

In this study, ab initio density functional theory calculations were performed on ATiO3 (A = Mn, Fe, Ni) materials for multiferroic applications. Structural, magnetic, electronic and topological analysis were investigated as regard the A-site cation effect. Concerning the prediction of new multiferroic candidates in silico, the role of different exchange-correlation functionals was reviewed. From such properties was verified that PBE0 functional performs the best for ATiO3 compounds overcoming the deficiency of standard LDA and PBESol functionals and get the better of B3LYP, PBE0+D and B3LYP+D. Regarding the A-site cation effect, calculated structural parameters follow the ionic radii trend moving from Mn to Ni, resulting in more ordered AO6 clusters; while, the TiO6 distortion increases. Using magneto-structural and magneto-electronic parameters, the antiferromagnetic exchange coupling constant was rationalized from GKA rules. The increase of the antiferromagnetic order along the transition metal series was explained from the 3d orbital occupancy and A–O bond interactions. DOS and band structure profiles clarify the semiconductor behavior as regard the 3d crystal field splitting for both A-site and Ti cations. Further, electronic results suggest the existence of intermetallic connection (A–O–Ti–O–A); whereas, topological analysis in the framework of quantum theory of atom in molecules was carried out to evaluate the A–O and Ti–O bond interaction through the analyses of ∇2ρ sign at bond critical point and of the charge-transfer parameter obtained from net charges.

Theoretical investigation of optical and structural properties of Ba-doped ZnO material

The doping process is a technique widely used for improving the properties of semiconductors. Through insertion of doping controlled amount is possible change drastically the electronic, optical and structural properties of a material. This work focuses on effects of Ba atoms insertion on wurtzite-ZnO structure at 12.5% amount. The results showed that the presence of Ba in low quantity cause increase in the lattice parameters and decrease in band- gap in relation to the ZnO material. In the percentage of 12.5%, the doping is noted as a potential alternative for application in opt-electronic devices, electronic devices, solar cells and photocatalytic process.

Theoretical investigations of the bulk modulus in the tetra-cubic transition of PbTiO3 material

Resulting from ion displacement in a solid under pressure, piezoelectricity is an electrical polarization that can be observed in perovskite-type electronic ceramics, such as PbTiO3, which present cubic and tetragonal symmetries at different pressures. The transition between these crystalline phases is determined theoretically through the bulk modulus from the relationship between material energy and volume. However, the change in the material molecular structure is responsible for the piezoelectric effect. In this study, density functional theory calculations using the Becke 3-Parameter-Lee-Yang-Parr hybrid functional were employed to investigate the structure and properties associated with the transition state of the tetragonal-cubic phase change in PbTiO3 material.

Experimental and theoretical study of the energetic, morphological, and photoluminescence properties of CaZrO3:Eu3+

In this study, we present a combined experimental and theoretical study of the geometry, electronic structure, morphology, and photoluminescence properties of CaZrO3:Eu3+ materials. The polymeric precursor method was employed to synthesize CaZrO3:Eu3+ crystals, while density functional theory calculations were performed to determine the geometrical and electronic properties of CaZrO3:Eu3+ in its ground and excited electronic states (singlet and triplet). The results were combined with X-ray diffraction (XRD) measurements to elucidate the local structural changes induced by the introduction of Eu3+ in the crystal lattice. This process results in the formation of intermediate levels in the band-gap (Egap) region, narrowing its width. The PL emissions were rationalized by characterizing the electronic structure of the excited singlet and triplet electronic states, which provided deep insight into the main structural and electronic fingerprints associated with [CaO8], [EuO8], and [ZrO6] clusters. In addition, the Wulff construction, obtained from the first-principles calculations, was used to clarify the experimental morphologies. These results extend our fundamental understanding of the atomic processes that underpin the Eu doping of CaZrO3.