Sergio Ricardo de Lazaro

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.

Fotoluminescência em materiais com desordem estrutural

The majority of the studies about photoluminescence had been carried out with crystalline materials, whose emission occurs at cryogenic temperatures, limiting the application of these materials. In turn, some amorphous solids, as titanates, tungstates, zirconates, among others, present photoluminescence at room temperature, seemed with silicon. This discovery led to the necessity of developing new models to explain the behavior of these materials. This revision intends to elucidate the results on photoluminescence, using a theoretical-experimental treatment, on the basis of the recent researches of this property in amorphous oxides.

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.

Propriedades eletrônicas e estruturais do PbTiO3: teoria do funcional de densidade aplicada a modelos periódicos

Calculations based on density functional theory at the B3LYP hybrid functional level applied to periodic models have been performed to characterize the structural and electronic properties of PbTiO3. Two different slab terminations (PbO and TiO2) have been considered to obtain and discuss the results of band structure, density of states, charge distribution on bulk and surface relaxation. It is observed that the relaxation processes are most prominent for the Ti and Pb surface atoms. The electron density maps confirm the partial covalent character of the Ti-O bonds. The calculated optical band gap and other results are in agreement with experimental data.

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.

Ba-DOPED ZnO MATERIALS: A DFT SIMULATION TO INVESTIGATE THE DOPING EFFECT ON FERROELECTRICITY

ZnO is a semiconductor material largely employed in the development of several electronic and optical devices due to its unique electronic, optical, piezo-, ferroelectric and structural properties. This study evaluates the properties of Ba-doped wurtzite-ZnO using quantum mechanical simulations based on the Density Functional Theory (DFT) allied to hybrid functional B3LYP. The Ba-doping caused increase in lattice parameters and slight distortions at the unit cell angle in a wurtzite structure. In addition, the doping process presented decrease in the band-gap (Eg) at low percentages suggesting band-gap engineering. For low doping amounts, the wavelength characteristic was observed in the visible range; whereas, for middle and high doping amounts, the wavelength belongs to the Ultraviolet range. The Ba atoms also influence the ferroelectric property, which is improved linearly with the doping amount, except for doping at 100% or wurtzite-BaO. The ferroelectric results indicate the ZnO:Ba is an strong option to replace perovskite materials in ferroelectric and flash-type memory devices.

Influence of the Bulk Growth Direction on TiO 2 and SnO 2 Surface Energies

TiO2 and SnO2 have the (P42/mnm) rutile structure with close lattice parameters and are extensively used in technological applications due to catalytic and optical properties. These properties can dependend on the surface directions and surface energy. It is of interest to estimate which directions are appropriate or energetically more favorable. Mathematical expressions often used in the literature to estimate the surface energy in oxides are based on a direct relationship between surface and bulk energies. However, for other workers the solid growth direction is represented only in the surface energy term (Esurf), whereas the bulk energy factor (Ebulk) has no influence of the solid growth direction. The latter term (Ebulk) is important for surface growth direction of a solid because both surface and bulk can grow in the same direction. This objective of our work is to investigate the influence of the bulk energy term (Ebulk), traditionally used in the literature, as well as the supercell energy term (Esupercell) representing the influence of the bulk growth direction on the surface energy of the solid. : Ceramic, crysta l, DFT, growth direction, rutile, simulation, SnO2, solid state, structure, supercell, surface energy, theoretical, TiO2.

Pb{sub 1-x}Ca{sub x}TiO{sub 3} solid solution (x=0.0, 0.25, 0.50, and 0.75): A theoretical and experimental approach

In this paper we report an experimental and theoretical study based on a periodic density functional investigation into selected compositions of Pb1�xCaxTiO3 x = 0.0, 0.25, 0.50, and 0.75. Based on our findings, we propose that the pseudocubic structure of these perovskites presents a long-range tendency for cubic symmetry, while the short-range displacements bring the solid solution to a tetragonal symmetry. The results are discussed in terms of x-ray diffraction, structural optimized parameters, Raman spectroscopy, band structure, density of states, Mulliken charge, and overlap population.